Abstract: The impacts of Brexit are particularly important to investigate in an area of shared competence such as the environment, which prior to the 2016 EU referendum had witnessed extensive and seemingly popular Europeanisation. To that end, this paper develops and tests a refined theoretical account of de-Europeanisation to assess how well it explains how and why UK environmental policy became increasingly differentiated after 2016. Drawing on an original analysis of relevant policy documents, parliamentary processes and legal reforms, it reveals how policy, politics and polity have changed more significantly than was originally foreseen. It departs from the existing literature by revealing that the devolution settlements of the late 1990s have opened up the possibility of not one, but multiple pathways of change ranging from de-Europeanization, through to dis- and active re-engagement. Outside the framework of EU processes and institutions, it shows that UK policy is being re-shaped via a multi-level negotiation between actors in Brussels, London and the devolved administrations. This negotiation has witnessed attempts at de-Europeanisation in England but active re-engagement in Scotland. It concludes that despite conflicting policy objectives across the UK, the predominant pattern of change is nevertheless one of gradual disengagement from the EU environmental rule-book.