Coastal erosion is a problem around much of the coast of Great Britain. This paper uses the example of Birling Gap in East Sussex to highlight a variety of problems associated with property boundaries on eroding cliffed coasts. The legal foreshore definitions (generally owned by the Crown) from English and Scots laws are compared with the use of tidal data from the nearest reliable tide gauge at Newhaven. With a Microsoft Excel spreadsheet model and shore profiling, these data are used to identify the extent of private property in the coastal environment at Birling Gap under both Scots and English law. The paper highlights that under both definitions, a small parcel of “land” exists at the base of the cliffs that is owned by the adjacent cliff top landowner. Therefore, the foreshores as defined in (Scots and English) law on the mainland of Great Britain do not fully enclose the envelope of coastal processes. Under Scots and English law, the foreshore is defined on the basis of tidal heights, irrespective of the mobility of the substrate that the foreshore boundary is drawn on. The cliff morphology at Birling Gap strongly suggests control by marine erosion; however, the tidal data from Newhaven suggest otherwise when compared with the shore profiles. A number of reasons are identified to explain a substantial difference in the height of the beach at Birling Gap and the observed tidal heights at Newhaven, including the distance from the tide gauge, the damping effects of tide gauges, and the morphology of the beach. We conclude that, under British property laws, a small area of the upper beach (which regularly changes in shape and size) is owned by the adjacent landowner and is technically under their control despite being regularly inundated by the tides.