Developing a unitary patent system for Europe has been debated for over 50 years but never achieved. Nonetheless, a unitary patent package (UPP) for the current 25 EU Member States who wish to participate is now within grasp. However, as this system neared completion, the UK voted to leave the EU by referendum on 23 June 2016. The UK subsequently triggered Article 50 TEU on 29 March 2017 commencing its withdrawal from the EU (Brexit) in a process expected to take two years. Beyond the broader legal and political questions which Brexit gives rise to, it raises a key question for patent lawyers, namely, whether, and under what circumstances, the UK can continue to participate in the Unified Patent Court (UPCt) system and European Patent with Unitary Effect (EPUE) when it leaves the EU? In November 2016, despite the Brexit vote, the UK government confirmed its intention to join the Agreement on the Unified Patent Court (AUPC) — and subsequently ratified the AUPC on 26 April 2018. However, this article argues that in light of the complex relationship the UPCt has with the EU, including, the primacy of EU law in the operation of the UPCt and links between the UPCt and the Court of Justice of the European Union (CJEU), joining the AUPC at this point is a curious move and one which is inconsistent with the UK’s previous more general statements on Brexit. In particular, in February 2017 Theresa May while outlining key facets of Brexit stated that the UK would not be subject to the jurisdiction of the CJEU once it leaves the EU. The article highlights the difficulties with ameliorating this position with the UK’s continued participation in the UPP post-Brexit. It argues that Brexit will likely sound the death knell for the UK’s membership of EPUE. Moreover, although UK participation in the UPCt seems more likely there remains considerable challenges to tackle in this respect. Furthermore, the question mark that exists over the UK’s participation in the UPCt and EPUE post-Brexit has attendant consequences for the general feasibility of the UPP. Accordingly, this article argues that instead of focusing on how to keep the UK within the currently devised system, Brexit provides further impetus to pause and consider whether the current proposal is still worthwhile given that it will create a more complex and fragmented European patent landscape at the supranational level. Instead, this article echoes calls that a better solution would be to consider ways to modify the current system or redesign a new system to include not just the UK but also other European Patent Convention states which are not in the EU.