The creation of agencies is a growing feature of contemporary governance yet key questions about agency autonomy and their influence on policy making remain unanswered. This article operationalises a policy network approach to explore the impact of agentification in three British government departments. It argues that the transfer of resources from departments to agencies created differing power-dependent networks between minister, department and agency. The networks have had both intended and unintended impacts on policy outcomes. Agencies have input to policymaking, the network's level of integration affects how well policies are delivered, networks have developed policy preferences and acted to impede further institutional change. These findings assist in understanding the nature of agencies' autonomy, the diversity of their impact on the policy process, and provide insights for other forms of alternative service delivery.