This article approaches the question of post-Brexit access of European Union (EU) Member States to the United Kingdom’s (UK) territorial sea fisheries by first discussing the pre-Brexit legal status quo under the Common Fisheries Policy (CFP) of the EU. Second, this article discusses the international legal framework for access to territorial sea fisheries that would apply if the UK withdraws from the EU in the absence of a future agreement. As Part II of the 1982 United Nations Convention on the Law of the Sea (UNCLOS) does notcontain provisions on fisheries access, this analysis focuses on the role of the 1964 London Fisheries Convention (LFC), bilateral voisinage agreements between the UK and EU Member States, potential acquired historic fishing rights of EU Member States in the UK’s territorial sea, and potential access rights derived from royal privileges. Next, this article addresses the relevance of the transitional arrangements contained in the latest draft withdrawal agreement of 2018, which was not, however, adopted by the UK. Finally, this article offers some conclusions as to the applicable legal framework for access of EU Member States to the UK’s territorial sea fisheries absent a new fisheries agreement between the EU and the UK, and potential ways to proceed in the future regulation of this issue.