Murder on Waterloo Bridge: placing the assassination of Georgi Markov in past and present context, 1970 - 2018

ABSTRACT In 1978, Bulgarian dissident writer Georgi Markov was murdered on Waterloo Bridge by an unknown assassin. The brazen attack in central London, Markov’s public profile and the alleged use of an exotic spy gadget (a poison umbrella) made the murder one of the Cold War’s most infamous cases of political assassination. However, despite wide-spread suspicions the case formally remains open, with the British government taking only limited actions against Bulgaria, the presumed culprit. This article draws on recently declassified archival materials from the United Kingdom to provide the first historical account focusing on the British dimensions of the case. The article discusses Markov’s journey to London, his murder and the British government’s response. It argues that the limited response to Markov’s murder largely followed uncertainty regarding the identity of the assassin and culpability of the Bulgarian state, as well as the political climate in the twilight years of détente. In contrast, British authorities responded tentatively to the attack on Litvinenko in 2006 and much more decisively to the attack on Skripal in 2018. This was due to the step change in the information environment providing more actionable intelligence and increasing unwillingness to accept Russian belligerence on UK soil.


Introduction
On 7 September 1978, as leader of the Bulgarian Communist Party Todor Zhivkov celebrated his 67 th birthday, Bulgarian writer, émigré, and dissident Georgi Markov was poisoned in London. Markov died days later-murdered in broad daylight in the centre of one of the world's busiest capital cities. As one of the most infamous assassinations of the Cold War, Markov's killing has been widely discussed. Indeed, the broad events leading to Markov's death are well understood, particularly since defections and the collapse of the Soviet Union allowed a number of former KGB officials to recount their stories. Moreover, the collapse of communism and opening of previously restricted Bulgarian state archives has allowed unprecedented insight into the case and likely identification of Markov's murderer, despite the destruction of many potentially relevant documents. 1 Decades later, the high-profile poisonings of Alexander Litvinenko (2006) and Sergei Skripal (2018) are both reminiscent of the Markov assassination. All three were UK-based exiles who were poisoned by hostile powers with exotic substances. Indeed, the continued use of poisons on UK soil and against naturalised British citizens renders a re-examination of the Markov case timely, particularly when comparing the differences in responses by the UK government: in contrast to the somewhat muted British response to Markov's murder, the UK gained increasing confidence after the murder of Litvinenko, exhibiting a forceful and robust response to the attempted murder of Skripal. To understand the British government's restrained response to Markov's murder, this article uses files from the British National Archives, contemporary reporting, and other sources to piece together an account of the Markov case from the perspective of UK authorities. In doing so, the article seeks to place the murder in past and present context.
The article makes a novel contribution in three main ways: first, it explores the British side of the story. While other works-both by former intelligence officers and historians-have considered Markov's murder, the article presents the first account of the British response to Markov's murder drawing on declassified British government documents. 2 In doing so it seeks to present a detailed historical account that looks beyond existing works that have largely focused on trying to tell the story of the intelligence operation using Bulgarian and Soviet files. 3 The article considers whether the available British files are able to provide new insights into the identity of Markov's killer. Second, the article is one of the first scholarly works to link together the three cases (Markov, Litvinenko and Skripal) to further our understanding of the British government's response to state-sponsored assassination on British soil. The most detailed existing accounts of these murders and attempted murder consider the cases in isolation, while others have focused on UK-based assassinations more broadly. 4 Third, the article also seeks to speak to more recent discussion of covert action-often considered as 'plausibly deniable intervention in the affairs of others'. 5 The article illustrates that while deniability of Russian involvement became increasingly 'implausible' in the more recent Litvinenko and Skripal cases, Bulgarian and Soviet involvement-although never fully confirmed-was also implausibly deniable in relation to Markov's murder in the 1970s. This supports recent work that highlights that plausible deniability 'barely existed' even in more historic cases of covert action. 6 The article begins by exploring Markov's journey to London, before recounting the Waterloo Bridge incident and his death. The article then considers the British government's response to the murder, highlighting the challenging nature of the investigation, limited witnesses and evidence, and the role of luck in identifying the murder weapon. The lack of concrete conclusions as to the identity of the assassin(s) and their sponsors, as well as a desire not to jeopardise Anglo-Bulgarian relations during the twilight years of détente, are argued to have been key in understanding the limited British response to the murder. This contrasts with the response to the twenty-first century cases of Litvinenko and Skripal where the greater availability of information, a spate of similar Russian assassinations in the UK and elsewhere, and an overall decline in Western relations with Russia have led to an increasing intolerance to Russian belligerence internationally and within the UK. In short, the different specifics of the murder weapons, the information environment, and the diplomatic context have shaped the British government's more extensive response to the cases from recent years.
Georgi Markov: writer, émigré and broadcaster,  Prior to his emigration to the UK, Georgi Markov was a novelist and playwright in his native Bulgaria-a communist police state. Although he originally trained as a chemical engineer, Markov began writing in the late-1950s, and began to gain popularity in the 1960s. In Bulgaria, he walked a fine line. Famous and influential, Markov could often be seen as part of Zhivkov's inner circle 'not in any official capacity but just as himself, a close friend of Zhivkov and his family'. 7 The close relationship with Zhivkov's daughter, Minister for Culture Ludmilla Zhivkova, gave additional protection as well as access to the lives of top officials. Indeed, as one account notes, Markov collaborated with the Interior Ministry's own literary group which was supervised by Colonel Kostadin Kyulyumov who helped found the Sixth Directorate of the Bulgarian Committee for State Security (Komitet za darzhavna sigurnost: KDS)-Bulgaria's Political Police. Consequently, 'Markov had access to top-secret files to aid his work on revolutionary novels and screenplays aimed at bolstering a "heroic" official vision of the State Security forces'. 8 As noted by fellow writer, Iron Curtain émigré, and friend Arkadi Vaksberg, it is this closeness with the ruling elites and his 'privileged and direct, not second hand, insight' that made Markov's writing stand out. Indeed, Markov 'spoke of the deception, hypocrisy, brutality, and corruption in the ranks of the governing elite and described its lifestyle and daily doings'. 9 Through the 1960s Bulgaria saw a 'thaw in artistic constraints', where the increasingly famous Markov seemed to push the boundaries of what was acceptable satire. 10 Notably he wrote a play called 'The Assassins' about a plot to kill a general in a police state and lost Zhivkov's support. 11 Markov's work began to attract greater scrutiny and later his highly critical play 'It was me' was banned. It was perhaps, as Vaksberg notes, 'the final straw that caused [Zhivkov's] patience to snap', and after a single private showing in Sofia in front of the party and government elite, the audience showed their outrage at the play's sarcastic tone. 12 It was in these circumstances that Markov left Bulgaria for Italy in 1969, ostensibly to visit his brother and to work on a film. Although he seemingly hoped that his relationship with the Bulgarian government might improve, rather than return home he stayed abroad: in 1970 he moved to London, and in 1971 Bulgaria refused to extend his passport. 13 Around this time he started work at the BBC as a programme assistant-as well as doing some work for Radio Free Europe (RFE). 14 In July 1972, Markov was tried in absentia in Sofia by a panel of three special judges. He was charged with defection, and putting himself at the service of a foreign country through his work for the BBC. 15 Markov was found guilty although, in contrast to the Soviet Union, Sofia's policy towards émigrés was much softer than Moscow's. After the trial, Markov was sentenced to six-and-a-half years in prison and had all his property confiscated. Indeed, this sentence may have been lenient even by Bulgarian standards with a high-level Bulgarian official later noting how anyone who overstayed their leave of absence from Bulgaria by more than three months was automatically indicted and liable to 10 years imprisonment. 16 Perhaps hinting at what was to come, that same official also noted that that Markov had been condemned as a traitor. 17 Throughout this time, Markov continued to live and work in the UK. In 1977, Markov applied for British citizenship although the Home Office allegedly deferred a decision on his application for a year. 18 He was working on satirical book about a chimpanzee becoming Prime Minister of the UK when he died in 1978. 19

Broadcasting dissent
At the BBC in London, Markov worked in the 'Bulgarian Section' of the external services, which included around ten Bulgarian staff. 20 The Bulgarian service broadcast three times a daydawn, tea-time and late-for a total of around 105 minutes, including a news bulletin and segments about current affairs. 21 However, it was likely Markov's work for RFE that provoked his assassination. Beginning in the mid-1970s, RFE started to attract the increasing ire of the Bulgarians and the wider communist bloc. Here, a new generation of authors such as Georgi Markov, Asen Ignatov, Dimitar Inkiow, Atanas Slavov and Vladimir Kostov helped define a new phase of influence for the station. Previously, broadcasts were led by 'old' émigrés who were staid and out of touch with modern realities of life back home. As such, they were relatively ineffectual in influencing the Bulgarian public. 22 However, as noted by Baev, these new writers helped provide 'detailed knowledge of the Communist elite's day-to-day life and secrets, and their names and work were widely recognised by the Bulgarian public'. 23 The addition of new talent also coincided with a change in RFE's approach to propaganda, including the broadcaster's 'more flexible approach' to events in the country, wherein by 'Moving away from direct challenges, RFE adopted a more "balanced" approach to news coverage, competing with official Bulgarian media, and attempting to exemplify radio journalism'. 24 This move away from overt propaganda towards a seemingly more balanced reporting combined with new blood was deemed to be highly effective.
The first available documentation of Markov in the remaining files of the Bulgarian archives appears in 1974 and between 1975 and 1978, Markov began his weekly broadcasts of Reportages in Absentia. 25 As Bulgarian documents show, the period saw increasing exchange between Bulgarian intelligence, the Soviet KGB, and other fraternal agencies on how to counter RFE. Indeed, in February 1976, the topic of dealing with RFE and Radio Liberty (RL) formed the centrepiece of a meeting between these agencies. 26 As an East German document noted following the meeting: 'International public opinion has to be mobilized for the purpose of ending the criminal activities of RFE and RL as hotbeds of ideological subversion whose existence is in contradiction with international law and the Helsinki final act'. 27 In 1977, a Bulgarian interior ministry document, further notes the regime's annoyance with the BBC: 'The BBC radio station has been the most active in the preparation and broadcasting of materials of anti-Soviet character of a constantly increasing number. At the end of the year, the broadcasts on this topic reached 36% in the various programmes'. 28 The Zhivkov regime clearly had an axe to grind-and Markov seemed to be at the epicentre of their annoyance. As Markov's friend Vaksberg notes, Zhivkov, 'The vengeful man at the tip in Bulgaria was deeply offended and could not forgive Markov for what he had done'. 29

Investigating the Waterloo Bridge incident, September 1978
On 7 September 1978, as he queued for the bus on Waterloo Bridge, Markov had a strange encounter with a passer-by on his way to work. He later began to feel sick and was unable to broadcast that night. The following day, the family doctor was called and Markov was admitted to St. James Hospital. On 9 September, Police were unable to interview Markov due to his deteriorating condition. The following day Markov continued to deteriorate, suffering from acute septicaemia and renal failure, and on 11 September at 10:50am he died.
After his death, the seriousness of the incident became clear. A 12 September police report provides an insight into what were believed to be early details of the incident. Though the details of the report would later prove to be incorrect, police initially thought that Markov left Broadcasting House at 6:30pm and returned around a half hour later. After returning, he spoke with his colleague fellow Bulgarian émigré Theodore Lirkoff, and is reported to have: complained that whilst in the Aldwych en route to Waterloo, a man, who spoke with a thick foreign accent, had jabbed him in the right thigh with an umbrella. He was feeling faint and asked Lirkoff to examine the wound, which he did, and saw only a small red spot which was slightly swollen. 30 After recounting Markov's biography and sentence in absentia, the police report concluded that 'in view of the possible surrounding implications', the investigation into Markov's suspicious death was to involve the Anti-Terrorist Branch of the Metropolitan Police (colloquially 'the Met'), and would be led by Commander James Nevill. 31 Nevill was a seasoned Met detective, having been involved in the investigation of the Great Train Robbery in the 1960s, and had become a familiar face to Londoners as part of the Scotland Yard bomb squad during the IRA's mid-1970s bombing campaign. 32 He had a reputation as a capable pair of hands.
On 12 September, Markov's post-mortem was conducted by a Home Office pathologist. The police report noted: 'A small puncture wound was found in the right thigh. The inquest revealed no apparent cause of death but investigation of body specimens will continue. Certain specimens are being conveyed to C.D.E. at Portadown [sic]'. 33 The Chemical Defence Establishment (CDE) at Porton Down was a Ministry of Defence (MOD) research facility that had conducted research on offensive chemical and biological weapons after the Second World War, but later focused on chemical and biological defence. Although staff at Porton Down would go on to find a small metal sphere in the sample provided, 34 Dr David Gall, the Research Medical Officer at CDE recalled the discovery in a lecture to the Royal Society of Medicine, detailing how the tiny fragment was almost missed: We were deciding where to take a piece for our work and I saw that Rufus [Crompton, the doctor who carried out the autopsy] had put in a pin to keep his orientation on a piece of loose tissue and had pushed it to the hilt, obviously to give him some kind of mark. Idly, as one does, I just tipped this with my gloved finger to make sure that that was what it was. To my alarm, this pinhead moved an inch across the tissue; it was a loose piece of metal. It was really very lucky that it did not roll off the post-mortem table on to the floor, under the cupboard and down the drain . . . 35 He describes the further examination of the pellet-telling how it was almost mistaken for a 'metallic bead that you sew on to a woman's handbag', although: . . . on examining at it more closely it seemed to be solid and the holes were equatorial. As far as I could make out, there were two holes drilled at right angles to one another through this little pellet. Through one I could see daylight, through the other I could see nothing, as there clearly was a lot of congealed tissue inside. 36 The pellet was so small that one Met forensic scientist recalled dropping the pellet on the floor multiple times in trying to examine it, and having to scrabble around on his hands and knees to find it again. 37 As the forensic investigation proceeded, the Met reconsidered more carefully the exact sequence of events. Following up on initial reports that Markov had been jabbed with the umbrella at the Aldwych on the North side of Waterloo Bridge, as per Lirkoff's story, the police struggled to find a single witness as they asked around the bus queues of the Aldwych. 38 Press reports around 19 September-12 days after Markov was poisonedsuggest a change in focus, with police seeking witnesses from the south side of Waterloo Bridge near to the Royal Festival Hall. 39 This delay in canvassing the correct area undoubtedly affected the trajectory of the investigation, drastically reducing the chances of finding any reliable witnesses.
By 24 September, according to press reports, 50 people had responded to the new appeal when the Met revised the timeframe. 40 According to reports, it was a betting slip obtained when Markov put money on a horse, that narrowed down the timeframe. 41 A later version of the Police report noted the changed location: 'subsequent enquiries by police indicate that the attack probably took place at around 1.50pm . . . when after parking his car, he was at a bus stop on Waterloo Bridge [on the South Bank] waiting for a bus, to take him to the Strand' on the north side of the river. 42 According to Nevill the new witnesses could not provide a description of the assailant. As he would note even six months later: 'We've come up with an absolute blank'. 43

A French connection: Kostov and a similar sphere, September-October 1978
Nine days before the Waterloo Bridge incident, on 28 August 1978, another Bulgarian defector and RFE journalist, Vladimir Kostov, was attacked on the Paris Metro. Prior to his 1977 defection, Kostov was a Bulgarian intelligence officer working undercover as a journalist in Paris. According to Kostov, he was exiting the Metro at the Arc de Triomphe stop when he heard a 'muffled crack', like an airgun, and felt a sharp sting in his lower back on the right side just above the kidneys. 44 The stranger who appeared to jab Kostov was not carrying an umbrella, although he was carrying a small bag and could have had something concealed inside. 45 Kostov had a high fever for a number of days after the incident.
Having heard of the attack, as the Police report later stated, Met officers travelled to Paris and in collaboration with French police, interviewed Kostov. On 26 Septemberalmost a month after he was jabbed-'an object was surgically removed from the lower back of KOSTOV and brought to the Metropolitan Police Laboratory. The object was identical in size and composition to that removed from Markov'. 46 Analysis by the Met showed the pellets had diameters of within one 1/100 of a millimetre of each other, while the drilled holes were identical in size. 47 Kostov would later note that removal of the pellet had involved a surgeon cutting out 3-4 square centimetres of his flesh. 48 The Director of Porton Down would later note his staff's role in connecting the dots: 'It was one of my staff that discovered the first metal ball and initiated the recovery of the second from Kostov'. 49 By late September, fresh evidence from Kostov allowed new connections to be drawn in the case. As a Home Office official had shared with the Foreign and Commonwealth Office (FCO), the pellets-made from a platinum-iridium mix-found in Markov and Kostov clearly had contained an unidentified liquid, and a press conference was proposed because 'going public' might encourage others who have similar pieces of metal inside them to come forward. 50 However, officials had no delusions about the political implications of a press conference, suggesting it would give rise to further public speculation. Given the prevailing assumption that Markov had been murdered by an agent of the Bulgarian government, the FCO deemed it prudent that it should be ready to respond to calls to summon the Bulgarian ambassador. 51 However, the lack of evidence remained problematic with an FCO official noting how it also meant a lack of grounds for official complaint. Accordingly: I did not think there would be any question of an official protest to the Bulgarian Embassy, let alone more drastic action, since although there was a clear supposition that the Bulgarian authorities were responsible for Markov's murder, there was no evidence of this and no basis on which a protest could legitimately be made. 52 Nonetheless, this did not stop the British press from drawing connections to diplomatic skulduggery. Markov's killing, the Daily Express noted, was an act of 'the purest gangsterism', such that the government should 'clean out the embassies' and that it was 'an admirable time to put every suspected K.G.B. man in the Communist bloc embassies onto a plane home'. 53 As one Evening Standard columnist argued 'If Markov's death is found to be murder then I for one would support a vigorous protest, including expulsions if necessary'. 54 He continued: 'If anything the [Foreign Office] has been too restrained with the Middle Eastern embassies which are accomplices to murder in London'. 55 Other articles named an individual at the Bulgarian Embassy said to be the head of the intelligence station in London, one of two individuals who worked for Bulgarian intelligence in the city. 56 The line the FCO and Foreign Secretary David Owen proposed the government take, however, was less explicit. Although Her Majesty's Government (HMG) was concerned about 'terrorist activity', and the evidence suggested a clear link between Markov and Kostov, the lack of clarity over who the assassin was and the lack of evidence of Bulgarian embassy involvement, meant action could not be planned against the Bulgarian embassy. 57 Shortly before the press conference was convened, the Bulgarian Ambassador was summoned to the FCO, where he repeated assurances that the Bulgarian government was not involved, and received assurances from the FCO that the finger was not being pointed, with the caveat that in a liberal democracy the press would obviously continue to speculate. 58 Two weeks after the controversial press conference provided further details about the murder, in mid-October, Markov was buried in a churchyard in Dorset. Towards the end of the month, and some six weeks after Markov was attacked, FCO officials noted police investigations had still 'so far failed to produce any evidence to show who was responsible for Mr Markov's death'. 59

The murder weapon? umbrellas, ricin and uncertainty
Although the idea of a poisoned umbrella caught the media attention, the only solid evidence were the identical tiny metallic spheres embedded in Markov and Kostov. At the 29 September press conference, police reported that Markov had been murdered, shared information about the metal spheres extracted, and even pictures of them. A November police report includes the same basic details shared about the spheres. The sphere found in Markov was: . . . formed of an alloy material approximately a mixture of 90% platinum and 10% iridium, and appears to have been cast rather than machined. It was 68 thousandths of an inch in diameter (1.7 millimetres) with two holes, 16 thousandths of an inch in diameter, drilled at right angles. In actual size it was smaller than a normal pinhead. 60 The press conference came at the end of a fortnight of media speculation about the substance that killed Markov. Early reporting, just days after his death, suggested that the Police had engaged CDE at Porton Down, and the removal of the spheres from Markov and Kostov. 61 The release of dimensions of the pellets and the holes allowed for more informed speculation. The size of the voids in the spheres narrowed down the type of substance that could have poisoned Kostov, and killed Markov, and led reporters and experts to consider the precise substance used. 62 Behind closed doors Porton Down had gone through a similar process of elimination, considering Markov and Kostov's symptoms and possible poison candidates. Ricin was viewed as a candidate early on because a particular scientist at the facility had done earlier work on the toxin. 63 Porton Down conducted tests of ricin on pigs to see whether they exhibited the same symptoms as Markov. As Dr David Gall, the Research Medical Officer at the CDE noted, 'that pig suffered very much the same symptoms that Markov did . . . the complete picture was so similar to that of Markov that it was extremely striking'. 64 Gall, in a longer lecture to the Royal Society of Medicine in 1980, noted 'Let me dispose of the question of toxin in the tissues. We were not able to find any. It was disappointing. We felt that we had tried quite hard but the fact was that by no means could we demonstrate the presence of anything toxic, let alone identify it'. 65 The investigation, he noted, produced 'strong circumstantial evidence for ricin, but that we could claim nothing more'. 66 This runs contrary to popular belief which seems to suggests a high level of certainty that ricin killed Markov. 67 On 2 January 1979, the inquest was held into Markov's death in London. According to an FCO account, the coroner concluded a verdict of 'killed unlawfully', and that: Markov's death had resulted from the introduction of a vegetable toxin, Ricin, contained in a minute spherical piece of metal. He could not see any likelihood that it was an accident . . . Commander James Neville [Sic] of Scotland Yard, in giving evidence at the inquest, said that the Police still had no indication of who was responsible of how the pellet was administered. 68 An FCO letter from shortly after the inquest caveated the ricin finding, noting that 'there is no direct evidence to show that this was the substance used (the body breaks down the toxin without leaving any trace)'. 69 Writing days after the inquest, the Director of Porton Down shared some thoughts on the investigation with MOD colleagues. On ricin, he noted: 'There is nothing scientifically new involved. Ricin, the material that we thought is the most likely to have been used, has a well-established record of possible BW/CW [biological/chemical weapons] significance'. 70 The letter saw some discussion of what the evidence suggested for possible attackers. The Director noted, although the material could have been made available from: . . . 'a friend in the right research laboratory' the hazards involved in handling materials of this level of toxicity, and the probable sophistication of the means of attack, suggest to us that a Government Agency or highly organised terrorist cell would have had to be involved . . . 71 Furthermore, he noted that sustaining a complaint against a suspect government would be difficult given that any blamed government could 'attribute the attack to an extremist group not under their control'-essentially providing a layer of (im)plausible deniability. 72 As an FCO official noted, responding to these points, they all: remain rather academic unless the assassin is caught and shown to have carried out his attack on behalf of a government . . . As yet there appears to be no firm evidence of who was responsible for Markov's death. Even if the culprit were caught it seems unlikely that firm evidence implicating the Bulgarian or any other government could be produced. 73

Wilder rumours: A 'SMERSH-type' assassin on the loose in London?
Within days of Markov's death, the British press were speculating about the circumstances, possible culprits and motives, a situation further fuelled by information released by the police at the late-September press conference. 74 One commonality between almost all the coverage, however, was that it featured the Bulgarian government, the Bulgarian KDS and the Soviet KGB as the most likely culprits. The extent of these allegations-along with the clear motive for Markov's murder-went some way to making any Bulgarian denials of involvement implausible. While most press coverage pointed the finger-either explicitly or vaguely-some created a sense of a wider conspiracy, furthered by the Kostov connection, and events in the following weeks.
Just days after the connection was drawn between the Markov and Kostov cases and publicised by the police press conference on 29 September, the Simeonov case added to the intrigue. Vladimir Simeonov also worked for the BBC Foreign Service, after defecting from Bulgaria in 1971 while visiting London as a tourist. He worked with Markov at the BBC. On 1 October-days after the pellet was removed from Kostov and weeks after Markov's death-Simeonov was found dead at his home in Plaistow, East London. The press, predictably, connected the dots. An unsubtle statement, seemingly from Scotland Yard, certainly did not prevent speculation: 'We are treating this as a suspicious death in view of the recent murder of Georgi Markov'. 75 A number of papers featured articles speculating about wider conspiracies. The Daily Mail suggested the Scotland Yard knew a 'highly-trained assassin' was on the loose, while the Daily Express described him as 'SMERSH-type', in a reference to a former Soviet counterintelligence organisation, a moniker popularised by James Bond. 76 The Sun asked 'Has the poison brolly killer struck again?', while the Daily Mirror suggested Simeonov's co-presenter was now under armed guard. 77 Furthermore, the Daily Mail reported 'a sinister incident', alleging that 'a man who said he was a Bulgarian and that he feared for his life stopped a police Special Patrol vehicle in Oxford Street and asked for help'. 78 This press speculation has continued to inform the popular understanding of Markov's death. For example, authors such as Seagave (1981) and Volodarsky (2009) both portray Simeonov as a KDS plant, ordered to spy on Markov and others at the BBC. Supposedly silenced after Markov's death, both cite reported claims such as a distressed Simeonov on his final journey home, as well as seemingly wiped glasses and bottles, and unlocked doors at his home point to an apparent conspiracy. 79 However, the reality of Simeonov's demise, at least according to Foreign Office files, seemed to be less sinister-a fall down the stairs. As a FCO letter on 3 October notes: The Police have established that Simeonov died on Sunday 1 October. The immediate cause of death was inhalation of blood; but some small bones were broken in his throat. There is no damage to his heart or brain, and examination and X-rays of his body have not revealed any suspicious punctures or unidentified metal fragments such as those found in Markov and Kostov. 80 Furthermore, it stated: There is no indication that Simeonov's home was broken into. If he was attacked (and there is as yet no firm evidence that he was) his assailant could have already been known to him and therefore have been admitted as a matter of course; . . . this is no more than speculation. 81 While Simeonov's death appeared a coincidence, and no metal sphere had been found, some reporters continued to speculate about the bruising. 82 The press was gripped with spy fever, as reporters even reported on the heart trouble of another friend of Markov-a Russian émigré-who had been deeply affected by Georgi's death. 83 While the press, catering to the British public's thirst for intrigue, pushed the angles of a broader conspiracy and assassin on the loose, Bulgarian state media and the embassy pushed back on this narrative. Comment by Bulgarian state media, circulated by Bulgarian diplomatic missions in early October 1978, noted: The fantastic story about the poisoned umbrella, about the emigrant's death cause by bacteria and the "new bacteriological weapon developed and produced by the Bulgarians" gave such a liberty of the author's fantasy in spite of the contradictions that were easily sighted. 84 The report continued, noting agreement with the Daily Mirror that the story was 'too complicated even for a personality like James Bond'. 85 Repeated denials of involvement, especially expressed through regime-controlled media of a communist state, and against reporting both credible and not-so by the British media, were hardly plausible.

British efforts to limit diplomatic fallout, 1978-1979
If press coverage put pressure on the UK government to act against the Bulgarian government, that same press coverage was also prompting pressure towards the UK government to be more circumspect. The Bulgarian Embassy repeatedly stated that they were not involved, and expressed concern to the FCO about what was appearing in the press. Just three days after Markov's death, in mid-September 1978, the Minister-Counsellor at the Bulgarian Embassy called on his FCO counterparts and complained of press coverage including 'direct and insulting references to the Bulgarian leadership' and that the reports were 'potentially damaging to bilateral relations'. 86 The FCO officials noted they had little information about the case themselves at this point, wanted to limit any damage to bilateral relations, and 'could not of course do anything to control or influence the comments of journalists'. 87 The following day, a British official was summoned to the Bulgarian Foreign Ministry to hear a protest about the 'anti-Bulgarian campaign' in the British press, as well as 'constant threatening telephone calls from British subjects'. 88 As the Bulgarian officials requested British officials to draw media attention to positive stories in UK-Bulgarian relations, the British official noted that the Markov story seemed to be 'quietening down'. 89 Reviewing this request, Owen noted that 'It would be totally counter-productive for us to try to shift the focus away from the Markov affair'. 90 A couple of days later, Lord Goronwy-Roberts, the Minister of State for Foreign Affairs, noted 'The Bulgarians are already in a whirl. If the incident was political it may be unofficial. Hence their fury. It is important that the Bulgarian Embassy should not be molested'. 91 Furthermore, the following day in relation to a BBC interview, FCO officials suggested that Goronwy-Roberts avoid talking about Markov if possible. 92 The FCO clearly wanted to avoid damage to relations resulting from a scandal.
In late September, as British officials considered the implications of the press conference, Michael Palliser noted the Bulgarian Ambassador 'should be left in no doubt that damage to Anglo/Bulgarian relations seems quite unavoidable'. 93 Another official noted a wish to avoid the British government being seen to be 'whipping up the media' to accuse the Bulgarian state. 94 Following Simeonov's death, Bulgarian authorities noted the case was being 'used by the British press to damage the image of Bulgaria and British-Bulgarian relations'. 95 The Bulgarian government-throughout this period of controversy-also continually sought to be involved in the investigation into Markov's death. 96 The British government was wary about this prospect. As a Home Office official noted to a Scotland Yard Assistant Commissioner, 'It is difficult to see this offer as anything other than a public relations move by the Bulgarians designed to allay press speculation about their own involvement, or an attempt to discover how much we know'. 97 In December the Bulgarian ambassador was said to be 'indignant' at the lack of a response on the offer. 98 Spring 1979 saw renewed controversy surrounding a BBC Panorama episode on the Markov case. The Bulgarian embassy heard of the programme early on, and expressed concern to the FCO. The Minister Counsellor asked the government to do anything they could to 'prevent the programme taking place' or to 'bring home to the BBC' the possible effects on bilateral relations. 99 The FCO reminded the Bulgarians of the BBC's independence, and suggested they should have agreed to participate if they were concerned. Days later an official from the British Embassy in Sofia was called in to the Foreign Ministry over the Panorama programme, and told it would 'further nourish slanders' against Bulgaria. 100 In the documentary-broadcast on 9 April 1979-Markov's mother alleged that a 'high up' and 'important' man from Bulgaria known to Markov, who she did not want to identify, had called her and told her Markov was to be killed with poison on account of his work for RFE, with a decision taken at the highest levels. 101 The programme and its host did not point the finger directly at the Bulgarian state, although it presented a number of sources that did, presenting the KDS and its Soviet KGB overseers as the prime suspects. The programme also detailed the disappearances and suspicious deaths of a number of Bulgarian émigrés in Austria and Denmark. The programme interviewed defector KDS and KGB officers, who both suggested their former employers were behind the killing, the KGB officer describing the method as 'ridiculously sophisticated' and likely trying to 'please someone on the highest level'. 102 Such claims would later be borne out.
After the Panorama broadcast, Markov became the biggest issue in UK-Bulgarian relations, with Bulgarian officials unwilling to 'let the matter drop'. 103 On 13 April, the Bulgarian Deputy Foreign Minister summoned the British Ambassador and suggested that the government should have tried to shut the programme down: as the Ambassador recalled, 'The Bulgarian government believed that the FCO could, and should have tried to do so'. 104 The British were keen to avoid a diplomatic spat with Bulgaria over Panorama and Markov. The controversy came as HMG sought to boost economic relations during détente, with the existing relationship later being characterised by the then British Ambassador in Sofia as largely being built on cultural rather than economic aspects. 105 At the time he noted that the documentary was not helpful-slim circumstantial evidence and hearsay, alongside unnecessary and problematic secret filming in Bulgaria was essentially being used 'to convince us of what we already know: that the Bulgarian security authorities were the most likely murderers of Markov'. 106 The Panorama film made such a splash that Prime Minister Margaret Thatcher even requested a copy of the transcript several months after it aired. 107 In the end, the Bulgarians focused their ire on the BBC, with the Bulgarian Foreign Ministry withdrawing distribution of the BBC pamphlet 'Arts and Features'. But the spat did not escalate beyond that as the government still allowed the BBC to film the Bulgaria-England football match in June 1978. 108 Diplomatic strife over the murder clearly remained below the threshold of cancelling the international fixture of two countries' mutual national sport. HMG made efforts to limit the damage, as tension between the BBC and the Bulgarian government continued into the Summer of 1979. The BBC paid tribute to Markov in its annual report: The intensity of the struggle for men's minds in Eastern Europe and the importance attached to this issue in the Communist world were tragically highlighted by the murder, clearly at the hands of a sophisticated secret service, of George Markov, a distinguished member of the Bulgarian Service. 109 Attempts made by the FCO to persuade the BBC to drop the sentence from the Report were unsuccessful-as an FCO official noted, 'The BBC do not accept our advice!!'. 110

British evidence regarding the assassin's identity? 1979-1994
Although the mystery surrounding the identity of the umbrella assassin has never been conclusively solved, suspicion of Bulgarian secret service and Soviet KGB culpability has endured long after Markov's death. Following the collapse of the USSR in the early 1990s, few specifics about the operation have been obtainable from Bulgarian or Soviet files. The British files provide few further insights into culpability-unsurprisingly, they provide fewer than the limited Bulgarian files, and other accounts published after the end of the Cold War. 111 In the first months following murder, the FCO spent some time chasing its own tail as it explored the rumour that Bulgarian state media had broadcast a message shortly after Markov's death saying it would 'seek out and silence enemies whether at home or abroad'. 112 With the help of the BBC they explored possible programmes broadcast by state media. 113 A statement was found linked to the Bulgarian Minister of the Interior, who allegedly had noted: 'Our enemies are nowhere safe from our grip. We do not acknowledge any borders. The counter revolution must realise that there are no secure places of refuge for it'. 114 This had seemingly been reported by a German newspaper, likely quoted from state television, although the FCO could not find evidence of a specific broadcast. 115 Although a similar statement-albeit one less connected to enemies overseas-was found to have been made by the Interior Minister on 15 September, it seemed the original quote was actually obtained from the Yugoslavian Service of RFE. 116 In 1979, a British official based at the Embassy in Sofia noted, the first time that Markov's name had come up was in relation to BBC broadcasts that 'had (we were told) caused great anger at the highest level'. 117 It turned out that these broadcasts-intriguingly-involved Markov interviewing Vladimir Kostov and his wife. The official noted that this seems to have been around the time that Markov's brother, Nikola, was approached in September 1977 and warned of the threat to Markov's life. This call to Markov's brother in Italy, which noted that poison had already been brought into Western Europe, was highlighted in the 1979 Panorama episode. 118 A further 1979 document from an official in the FCO Eastern European and Soviet Department in London notes that the Bulgarian Deputy Minister of Foreign Affairs (responsible for cultural and information matters) protested over Markov's BBC broadcasts a little later than 1977, in January and April 1978. 119 The FCO official also asked: Why were the Bulgarians so worried about Markov? . . . The main reason for Bulgarian anxieties seems to be his former close acquaintance of the Bulgarian Head of State Todor Zhivkov. In fact I think we have no evidence to substantiate this relationship other than Markov's own statements. What is interesting is that Markov's activities in the West do not appear to have worried the Bulgarians too much between 1970 . . . and the defection of Vladimir Kostov in mid-1977 . . . it may have been that it was Kostov in fact who was the main target with Markov as a second string. However as it was Markov who was killed there has been a tendency to focus on his significance rather than that of any other Bulgarian émigré 120 These documents, far from providing a smoking gun on culpability, further emphasise the British government's uncertainty over events.
The British files extend some way into the aftermath of the Cold War. Weeks after the fall of Zhikov in Bulgaria, Markov was rehabilitated by the Bulgarian Writers Union, his works were to be republished, and prospects for a new investigation looked positive. 121 In December 1989, FCO Minister William Waldegrave called out the Bulgarian government as behind Markov's death in the House of Commons. 122 In January 1990, Waldegrave was asked by a Bulgarian journalist whether the British government was willing to assist the new Bulgarian government's Markov investigation. Waldegrave was noted to think that the inquest records and 'perhaps other secret material' should be made available to the Bulgarians. 123 Waldegrave's Assistant Private Secretary went on to ask senior FCO officials 'whether we should make available sensitive information which I understand goes some way towards identifying the killer'. 124 There may have been more specific information in the registry of British intelligence which came close to identifying a possible assassin.
Initial British efforts to assist with a new investigation in Bulgaria were unsuccessful. 125 In discussing possible information that the UK could share with a Bulgarian investigation, a February 1990 Home Office document outlines a difference between the 'intelligence assessment' and the 'criminal investigation'. 126 The intelligence assessment, it is noted, 'points to the conclusion that the Bulgarians were responsible for Mr Markov's death'. The letter continues: I say 'points' deliberately because as I made clear when we spoke there is no information available here, of which I am aware, which provides definitive grounds for linking Mr Markov's death positively with the Bulgarians . . . Bulgarian responsibility is an inference drawn from the sophistication of the attack -pointing to state responsibility -and the absence of any motive on the part of anyone other than the Bulgarians. It would not be accurate to imply to the Bulgarians that we have evidence -even of an intelligence nature -that they were responsible. 127 The letter continues: 'The strong feeling is that the answer to all this lies in Bulgarian hands'. 128 Some exchange was seen between the British police and Bulgarian prosecutors in 1990. The Met discussing using the name of a 'suspect' which had come up in the investigation, someone 'probably a member of the intelligence services', in order to see the Bulgarians' reaction. 129 The British files show that the government were aware of, and engaged with, new theories advanced by former KGB officers in the early 1990s. An unnamed intelligence source seems to have hinted to the veracity of Oleg Gordievsky's account in his 1990 book, and following this the British Embassy in Sofia ordered six copies of the book to share with local contacts. 130 According to Gordievsky, the poison and the modified umbrella used to kill Markov came directly from the KGB's Operational Technical Directorate (OTU), as did support in the form of KGB operative Sergei Mikhailovich Golubev. The operation to support the Bulgarian request is described as being personally approved by Head of the KBG's First Chief Directorate, Vladimir Kryuchkov himself. 131 Former KGB counterintelligence chief, Oleg Kalugin, whose description represents perhaps the most persuasive account of Markov's murder, supports Gordievsky's narrative and provides additional detail. Kalugin himself was arrested at London's Heathrow airport in November 1993 on a visit to London to film for a Panorama documentary about Russian intelligence. Ostensibly detained due to a misleading headline ('I Organized the Assassination of Georgi Markov') in the Mail on Sunday, Kalugin was questioned on the Markov case at a London police station before being released without charge the following day. 132 In his 1994 book 'First Directorate', Kalugin describes how the Soviet Union felt pressure to support a direct request from Bulgarian leader Zhivkov made in 1978. 133 Kalugin recounts a meeting in KGB Chairman Andropov's office with a number of senior officers. He recounts Deputy Chairman of the KGB, Kryuchkov, telling the group: 'They want us to help them in the physical removal of Markov. This request was made by [Bulgarian Interior Minister] Comrade Stoyanov, but it comes from President Zhivkov himself'. 134 After going back and forth as to whether to assist, Andropov is said to have concluded: 'All right, all right . . . But there is to be no direct participation on our part. Give the Bulgarians whatever they need, show them how to use it, and send someone to Sofia to train their people. But that's all. No direct involvement. I won't permit any more than that'. 135 Kalugin goes on to describe how the 'Bulgarians stumbled toward the assassination of Markov' in a 'wrenching trial-and-error process, right out of the pages of the blackest comedy'. 136 While British officials did receive some tips, and information from sources of unclear veracity, the documentary record-at least from the FCO and Home Office-suggests that Markov's assassin was perhaps suspected, but unknown. British intelligence clearly assessed Bulgarian responsibility on the grounds of capability and intention, but does not seem to have been able to point the finger at a particular individual with any real certainty. Likewise, the police investigation clearly had some suspects but lacked witnesses or other evidence. Indeed, in 1993, British police interviewed an individual -Francesco Gullino-who would later emerge in the late 2000s as the prime suspect after journalist Hristo Hristov's examination of declassified Bulgarian files, but could allegedly produce no evidence of his involvement. 137 Christopher Andrew's 2009 official history of MI5-released 31 years after Markov's killing-notes that Markov 'was murdered by Bulgarian intelligence, assisted by its Soviet allies', but provides no further details. 138 Whether this is based on documents in the MI5 files Andrew had access to, or rather just the most likely and popular theory, is unclear. 139 The methodological challenges in writing intelligence history and the limitations due to lack of access to material are well explored. 140 Even if documents in the Security Service archives do provide more insights into possible suspects, the publicly available archival record suggests that logic regarding motives and the sophistication of the attack, rather than any 'evidence' of a culprit, was what enabled internal intelligence assessments to conclude that the Bulgarians were likely responsible.

Echoes of Markov? Alexander Litvinenko and Sergei Skripal, 2006 & 2018
Almost 30 years after Markov's death, in 2006, and over a decade later in 2018, Russian authorities attempted the murder of defectors with sophisticated poisons on British soil. The first saw former Russian Federal Security Service (FSB) officer Alexander Litvinenko poisoned with radioactive isotope polonium-210 administered by Russian assassins using poisoned tea during a visit to a London hotel. 141 The second saw a Russian hit squad attempt to kill former Russian GRU military intelligence officer Sergei Skripal using a Novichok nerve agent smeared on the door handle of his home in the cathedral town of Salisbury. 142 These attacks are just two of more than six suspicious deaths between 2000-2019 involving Russian émigrés or connected individuals on British soil, and follow on from a long history of the use of poisons by the Soviet Union intelligence apparatus from the 1920s onwards. 143 Both attacks have clear echoes of the Markov affair. These include the more obvious: intelligence agencies seeking to murder purported 'traitors' in Britain, the use of novel poisons and delivery methods as murder weapons, and the attacks representing covert implausibly deniable acts purportedly signed off at the highest levels designed to instil fear in other dissenting voices and defectors. In doing so, such attacks seek to show that Russian dissidents are safe nowhere-not even in the relatively secure and comfortable environment of the United Kingdom. The three incidents highlight the challengesindeed perhaps the futility-of British efforts to protect a large number of dissidents and defectors 24/7 from foreign governments who may be determined to take their lives.
The British government's Markov files also highlight other similarities. All three attacks involved complex criminal investigations by British police and intelligence as they sought to identify the assassins, or would-be assassins, in order to bring them to justice. The files show that the Bulgarians were keen to get involved in the Markov investigation, just as the Russians were keen to involve themselves into the investigations into the attacks on Litvinenko and Skripal. This would have allowed them to shape the narrative and undermine the British authorities' search for the truth. As a Home Office official noted in 1978, 'their "assistance" would presumably be intended to frustrate rather than to further police enquiries'. 144 The Bulgarians sowed misinformation about Markov's death-labelling press stories an author's fantasy unworthy of James Bond. 145 However, this is hardly comparable to Russia's industrial-scale disinformation efforts after the Skripal poisoning in the information age, including a now infamous television interview on Russia Today. 146 Here, in some deadpan Wikipedia-based trolling, the two suspects, identified as Alexander Petrov and Ruslan Boshirov, went on air and claimed that they had gone to Salisbury to visit its Cathedral, which is 'famous not just in Europe, but in the whole world. It's famous for its 123-metre spire, it's famous for its clock, the first one [of its kind] ever created in the world, which is still working'. 147 There were, however, also clear differences-particularly in the British government's responses. In the Litvinenko and Skripal poisonings, suspects were publicly named within weeks of investigations opening, extradition requests were made and, in the case of Skripal's attackers, an unprecedented expulsion of 153 Russian diplomats by the UK and its allies. 148 In comparison, the response to Markov's murder was limited to diplomatic protest and the cancellation of the BBC 'Arts and Features' pamphlet. Football coverage was unaffected. Indeed, comparing the incidents suggests the more assertive response to more recent poisonings were the product of two primary factors, namely the changing information environment (including the signatures of the poisons used), and the increasing intolerance of British officials to Russian belligerence on UK soil.

The information environment
One of the main limiting factors as shown by the Markov files was the lack of concrete intelligence or evidence regarding Markov's assassin-there were no real witnesses, and no credible description. This clearly hampered British authorities from pointing fingers at Soviet and Bulgarian authorities as 'Although there is no evidence which would stand up in court and, indeed, no individual as a suspect, it is difficult to conceive of any other credible explanation'. 149 Moreover, the Markov investigation got off to a slow start where, because of initial accounts, the Met only approached possible witnesses in the correct location almost two weeks after the incident.
This contrasts with the more recent events where more capable state intelligence agencies-the UK's and others-alongside state scientific and technical establishments, and the evolving public information landscape allowed for more definitive identification of perpetrators. For example, in the Litvinenko case, the polonium-210 took approximately 20 days to kill Alexander Litvinenko, who received intensive medical care after falling seriously ill. During this time, Litvinenko was also able to debrief police officers. As a former intelligence officer who routinely took detailed notes, Litvinenko himself was able to provide detailed information, including naming Andrey Lugovoi and Dmitry Kovtun as key witnesses. 150 Indeed, Litvinenko's testimony would provide key insight into the events leading to his death, as would the poison agent used.
Unlike ricin which breaks down in the body, polonium-210 is also persistent and its radioactive signature provided a huge amount of evidence to those tracking Litvinenko's killers. In fact, the polonium left a literal radioactive trail from the hotel bar where Litvinenko was poisoned, through the suspects' hotel rooms, and even back to Moscow on a British Airways aircraft. 151 Thanks to the realisation that key suspects would be unlikely to face criminal proceedings-and the perseverance of Marina Litvinenko-on 13 October 2011 the previously delayed inquest into Litvinenko's death was resumed, and Sir Robert Owen was appointed to conduct the inquest on 7 August 2012. The inquest allowed for unprecedented levels of scrutiny and, in 2016, Sir Owen's report concluded in a legally significant judgment that polonium used in the attack 'unquestionably' originated in Russia, and that 'The FSB operation to kill Mr Litvinenko was probably approved by [FSB Director] Mr Patrushev and also by President Putin'. 152 Nonetheless, critics of the British response described the UK's response as 'late, lame and lamentable', that sent a dangerous signal to Russia that the British response and resolve was weak. 153 Concerns over this lamentable resolve would combine with a radically different information environment and inform a newly robust UK response. Similar to Markov and Litvinenko, in the Skripal case prima facie evidence pointed towards Russian authorities. Although there were no direct witnesses of the poisoning besides the Skripals themselves, who were unaware of their exposure to the poison, after learning of their patient's identify British authorities were quick to begin their investigations. Skripal was found unconscious on 4 March 2018, and by 12 March the presence of Novichok had been identified and disclosed by Prime Minister Theresa May. 154 Similar to how the fact that global polonium production is centred in Russia lent weight to conclusions that the polonium that killed Litvinenko was sourced from Russia, testimony from former Soviet chemical weaponeers strongly indicate that Novichok chemical weapons are also of unique Russian design, despite a subsequent medley of implausible claims, including that research on novichok took place globally (specifically in the Czech Republic, Sweden, the UK and in the US) and that various laboratories in the Baltic States also retained this capability. 155 This allowed May to credibly argue that Russia was the source of the poison, outlining two alternatives: either that Russia had ordered an attack using chemical weapons in the UK, or that Moscow had lost control of such weapons. 156 Such conclusions could not be drawn in the Markov case because, although ricin and the microscopic pellets were sophisticated, British authorities were unable to rule out other possible, although perhaps not credible, alternatives to Sofia and Moscow.
In addition to the strong Russian association with the poisons used against Litvinenko and Skripal, increased use of CCTV and other electronic data has transformed the information environment since the 1970s. This allowed British authorities to publicly identify the two Russian suspects and their movements within the UK. The public announcement of this came on 5 September 2018 and was the product of reviewing 11,000 of hours of CCTV footage and taking more than 1,400 statements. 157 To this end, May outlined how police had established that two Russian nationals (travelling under the assumed names of Alexander Petrov and Ruslan Boshirov) entered the country at Gatwick airport, took two trips to Salisbury, and then left the country through Heathrow airport.
The fact that CCTV recorded the movements of the Russian hit squad from the moment they disembarked their aircraft already marks a considerable improvement upon the information available to the police investigating Markov's killer. However, beyond this, it is also notable that the 2000s saw a step change in the use of 'Open-Source Intelligence' or OSINT. To this end, non-governmental groups have used publicly available information to gain insight into areas traditionally dominated by 'closed sources' intelligence. 158 Indeed, following on from May's September 2018 speech, Bellingcat-a leading opensource investigative group-played a key role in identifying the GRU killers using OSINT and leaked Russian government databases, releasing their real names and involvement in other similar cases across Europe. 159 Identification of the perpetrators by non-governmental groups using such means would have been unthinkable in the early 2000s, let alone the 1970s.
In both twenty-first century cases, in spite of extensive Russian disinformation efforts, the British state and its allies were able to present a clear and detailed narrative encompassing the killers identities, the methods and the motives, building public cases for taking measures against Russia. This clearly contrasts with the Markov case where the paucity of evidence hampered the investigation. However, while the twenty-first century cases saw Russian acts that they could not plausibly deny, Bulgarian denials of culpability in the Markov case were also hardly plausible, with Bulgarian motives and press reporting making this the case.

British tolerance of foreign conspiracies: domestic and international drivers
Although the attack on Markov was a sensational event, it was hardly the first political murder on British soil, with some 18 significant assassination attempts between 1971-84 alone. 160 Indeed, by the late 1970s, London was 'recognised as a major global site for political murder', and towards the end of the decade the British state started to take a more systematic approach to countering assassination. 161 In 1978 under the Callaghan government assassinations started to be treated as 'occasional acts of violence that the state . . . needed to discuss and plan for', with a more joined up approach from key Whitehall departments. 162 It is against this context that Markov's death was investigated and a response formulated.
Despite the lack of firm evidence on which a case could be made to either the British public or foreign governments, the British government still clearly sought to balance the lack of evidence with public reassurance. Indeed, after internally acknowledging the lack of firm evidence, the Home Office noted that public pressure would likely demand a response, and that 'The government may well be asked what action it is taking to prevent murder on our territory'. 163 Officials referred back to Operation FOOT, the unprecedented expulsion of 105 Soviet officials-intelligence operatives-from Britain in 1971, which marked a 'major turning point' in British cold war counterintelligence efforts. 164 The expulsion of Russian operatives in Operation FOOT did not stem from any single acute incident, but rather a frustration with the blatant violation of diplomatic protocol by the Soviet Union, and the excessive use of its London missions to house Soviet spies.
Notably, Markov's death, while one of five high-profile assassination attempts in London in 1978 alone, was an anomaly in that the other four were Iraqi or PLO figures. 165 Five Iraqis had been expelled in July 1978 as a result of concern over a series of attacks on Middle Eastern targets in London, including the former Iraqi Prime Minister Abdel Razak el-Nayef, just weeks earlier. Markov's murder surprised, with one FCO official noting just months before his murder that the Soviets appeared to operate to a 'code of conduct' in London, unlike the Iraqis. 166 The Iraqi case illustrated the way that these types of activities linked to diplomats and embassies could lead to embarrassing press coverage-like the coverage of the Markov case discussed above-and resulting government concerns about pressure from the public and the accused embassy themselves. 167 A further domestic factor restraining the response-although difficult to calibraterelates to public views and media presentations of the victims' identities. Markov was a Bulgarian national at the time of his death, although he was exploring options for British citizenship. The Bulgarian aspect of his identity-as a famous Bulgarian dissident playwright-was a key part of the story reported by the press. This contrasts somewhat with Litvinenko, a naturalised British citizen, who was described widely in the press as British, having worked for British intelligence, and a 'Russian spy'. The inquiry report would describe his delight at obtaining British citizenship in the two weeks before he was poisoned, his pride, and even how he flew the flag of St George during the 2006 World Cup. 168 Skripal also held British and Russian citizenship, and the attack also resulted in the death of a British national who later found the poison perfume bottle. The British identity and nationality of the victims in these more recent cases, as well as press coverage about this, would also likely have pressed officials to take a more assertive response.
Despite a need to reassure domestic audiences, the limited response to the Markov killing was also in some way shaped by the international environment. The murder occurred in what would turn out to be the twilight of détente-a period where both sides carefully pursued better East-West relations, and a decrease of Cold War tension. Détente had been pursued as a policy by President Nixon from his election in 1969. 169 Under Ford, who assumed office in 1974 pledging to carry on Nixon's foreign policies, détente diminished and by 1976 the administration avoided use of the term. 170 When Carter assumed office in 1977 he sought to inject new life into détente, an effort largely relinquished within the first six months of his presidency. 171 Events of 1979-particularly the Soviet invasion of Afghanistan-proved to be the final nail in détente's coffin.
There is also little clear evidence in the FCO files that the US was consulted or that USrelated considerations affected the UK's approach to the Markov case. Reflecting the détente policy, the US relationship with Bulgaria did improve in the 1970s. 172 In 1977, however, Carter issued Presidential Directive/NSC-21 on policy towards Eastern Europe. The Directive noted that relations with Bulgaria would remain limited, with no active steps taken to enhance their international independence, or to increase internal liberalisation.- 173 There is no evidence in the British files of particular interest from the US in the Markov case or pressure to respond-this absence was notable given many files consulted were FCO files where a US diplomatic approach or interest would likely be evident, although undoubtedly there will have been engagement between intelligence communities on the case at the working-level.
Moreover, the UK's previous experience with 1971ʹs Operation FOOT strongly suggests a desire to keep efforts to deal with diplomatic malfeasance in-house. While the British government 'pursued détente, a little reluctantly at first, but then with genuine commitment', they were 'not afraid to confront where they felt their interests were at stake' highlighted by the 'confidence with which they executed their expulsion of 105 Soviet agents'. 174 In the post-FOOT atmosphere, British communications with the Soviets continued to talk up hopes for détente. 175 Washington was not informed of Operation FOOT until after the event. Indeed, there appears to be a lack of consideration as to how FOOT would affect the UK's relationship with allies-notably the US-in the documentary record. 176 Rather than upsetting a delicate East-West balance, Washington's main objection to Operation FOOT appears to have been the lack of consultation. 177 Had the UK seriously considered a more assertive response to the Markov murder, more diplomatic engagement with the US and other allies would likely be evident in the files. The UK clearly still did not want to risk damaging Anglo-Bulgarian relations in its response to the Markov case, as displayed in several quotes from correspondence above. The British approach to détente was effectively one of 'caution' and 'limited expectations' against efforts to balance between confrontation and cooperation. 178 As it drove restraint in the 1970s, the international context played a role in driving a more robust response to the more recent poisonings. The UK's response to Litvinenko and Skripal took place against backdrop of deteriorating relationships with Russia. In the wake of the 9/11 terrorist attacks in 2001, the West sought co-operation with Russia on a range of topics including counter-terrorism with UK government initially keen not to disturb the build-up of 'goodwill' between the two countries and continue strategic talks particularly in the area of trade. However, the response to Litvinenko's poisoning presented British authorities with a dilemma regarding competing economics and moral interests, with the government seeking 'to strike a balance between punishing Russia to deter it from further attacks and maintaining cooperative relations'. 179 An inquest into Litvinenko's death was initially opened on 30 November 2006, however the police investigation remained underway and the inquest adjourned pending the police investigation and any criminal proceedings. In May 2007, the UK's Crown Prosecution Service (CPS) requested that Russia extradite the chief suspect, Andrei Lugovoi, a request that was denied by the Russian authorities. As a result, the Labour government under Gordon Brown expelled four Russian 'diplomats' that authorities accused of being intelligence officers from the Russian embassy. In addition, the UK undertook an internal review of UK-Russian cooperation, suspended negotiations for a bilateral visa-facilitation agreement, tightened other visa arrangements and suspended official contact with the FSB. 180 The UK also held discussions with its European partners about coordinating EU-Russian relations 'although the EU's somewhat tepid response fell short of its hopes'. 181 In contrast to Brown's Labour government, Cameron's Conservative government prioritised economic considerations in Anglo-Russian relations. Despite his tough words regarding Russia's 2008 invasion of Georgia while in opposition, after becoming Prime Minister in 2010 David Cameron sought greater economic cooperation with Russia. For example, in a October 2010 speech to the Confederation of British Industry (CBI) Cameron lamented that the UK exported more to Ireland than to the BRIC countries (Brazil, Russia, India and China), promising that 'the promotion of British commerce and international trade' would be 'at the heart' of his government's foreign and economic policy. 182 Indeed, in November the following year, Cameron boasted how his government was 'loading up planes with British businesspeople and taking them to India, China, Russia, Turkey, South Africa and Nigeria'. 183 This came just months after the first face-to-face meeting between British and Russian leaders in September 2011. During this meeting, Cameron insisted he had not 'parked' concerns about Russia's poor human rights record, but instead focused on the £215m of business deals agreed with Moscow. Following the trip, then Foreign Secretary, William Hague, confirmed that his government had met its 'objective in coming here and expanding working relations at the top of government, reinforcing the opportunity for jobs, and for business'. 184 Economic considerations then influenced the Cameron government's handling of the Litvinenko case, as did wider fears of alienating Russia and the financial costs of a public inquiry. 185 As a result, the British Parliament's Intelligence and Security Committee would lament the fact that Litvinenko's death elicited a 'slow and isolated response to Russian aggression' compared to that shown against the Skripal poisoning. 186 Perhaps with this timid response in mind, the response to the Skripal attack was more immediate, seeing the UK eject 23 Russian 'diplomats' it claimed were intelligence operatives, alongside concerted action by 29 other states expelling over 150 Russian 'diplomats' in total.
The international normative and legal context also shaped the varied responses to the different poisons used. Although ricin has long been considered as a toxin with potential military utility, its difficulty in widespread transmission and localised effects mean 'most experts believe that ricin would be difficult to use as a weapon of mass destruction'. 187 Indeed, traces of ricin were never found by investigators. In contrast, the polonium-210 and Novichok are far more dangerous and potent. Both instances of use also resulted in numerous cases of secondary contamination and substantial decontamination costs. 188 Beyond the radioactive polonium trail left across London and further afield, Litvinenko's post-mortem was described by those undertaking it as probably 'the most dangerous . . . ever undertaken in the Western world', and the use of polonium posed some risk to the public with 700 people tested. 189 Twelve people in total suffered secondary contamination. 190 The Novichok agent, while placing Skripal and his daughter in a serious condition rather than killing them, did claim the life of one member of the public and make several other individuals very sick. Both incidents required extensive specialist clean-up operations. The use of polonium as a radiological poison was described by Litvinenko's wife as 'the first ever act of nuclear terrorism on the streets of London'. 191 The international significance of these incidents was clear to decisionmakers who investigated and responded to the poisonings. While the substances themselves were so obscure-possibly in an attempt to better disguise their use-decisionmakers were deeply conscious of the impact of their use on global norms against chemical and radiological weapons, even to poison on a limited scale. 192 Since 9/11, and particularly under the Obama administration, significant effort has been made to address the risk of nuclear and radiological terrorism. The use of a Novichok chemical weapon agent against Skripal came against a background of concern over rising use of chemical agents more generally. This stemmed from the use of chemical weapons in the Syrian civil war from 2012 to 2019 and Russia's subsequent diplomatic shielding of Syrian officials from international scorn, as well as North Korea's use of VX nerve agent to assassinate Kim Jong-Nam at Kuala Lumpur airport in 2017. A response to the Skripal poisoning was likely viewed as required by a need to push back on an eroding norm of non-use of these agents.

Conclusion
While the Markov case may appear to be an obscure episode of Cold War assassinationit clearly provides some insights for the present day. Parallels-and differences-can be drawn between Markov's assassination and the UK government's response to Litvinenko's murder in 2006 and the Skripal poisonings in 2018. A number of similarities have been explored in the article: intelligence agencies seeking to murder purported 'traitors' on British soil; the use of novel poisons and delivery methods; attacks representing covert implausibly deniable acts designed to instil fear among other defectors and signed off at the highest levels. Also in the investigations: long, complex and diplomatically perilous; highly complex scientific aspects; and a suspicious desire by the principal suspects to be involved.
The key differences have been shown to be the impact of the information environment on the British government's response. Analysis of archival material shows that throughout the period of Markov's death and the subsequent investigation, the British government was hamstrung by the lack of firm evidence with which to confront Bulgarian and Soviet authorities. Moreover, British authorities were keen to balance public pressures against diplomatic sensitivities. This made the response to Markov fairly limited.
In the wake of the 9/11 terrorist attacks, the West sought co-operation with Russia on a range of topics with the UK government initially keen not to disturb the build-up of 'goodwill' between the two countries and continue strategic talks particularly in the area of trade. This resulted in a muted initial response, and a delayed public enquiry into Litvinenko's death. A more extensive response was seen to Skripal in 2018, and to a lesser degree to Litvinenko as the enquiry concluded a decade after his death. This came against a background of worsening relations between Russia and the West. The use of highly toxic poisons, with wider collateral impacts and raising more concerning normative challenges, also provoked a greater response.
The twenty-first century information landscape made determining culpability easier in the Litvinenko and Skripal cases, with evidence showing the assassins' moves from entering the country to the target. The greater availability of information about the Russian culprits certainly made Russian denials surrounding the murder of Litvinenko and attempt on Skripal implausible. However, the clear motive, the circumstances and rampant media reporting around Markov's murder also made Bulgarian denials implausible, although perhaps to a lesser degree. In this regard, the Markov case supports recent research in the area of covert action that suggests that the concept of 'plausible deniability'-a phrase often associated with studies of covert action-was somewhat of an artificial construct. 193 The evolved information landscape that formed the context to the twenty-first century cases also made fighting Russian disinformation-much more extensive than that of Bulgaria in the 1970s-much more challenging.
The opening of the Cold War archives-albeit with many papers inaccessible or destroyed-still leaves some ambiguity around the identity of Markov's assassin and the precise motives surrounding the killing. This is the case even after analysis of what remains of the Bulgarian files. Still, far more is known about Markov's death now than before. Numerous testimonies from those involved in the planning of the operation, and the opening of previously-closed archives have helped shed some light on the motivations, the materials used, and people involved in the operation. This article has sought to add to the British side of the story. Rather than 'solving' the mysteries surrounding the Markov case, it has instead emphasised that the British government has long asked and failed to answer similar questions as external observers with regard to Markov's killing, and this goes a long way to explaining the limited response to high-profile murder on British soil.