Continuity as the rule, not the exception: How the Vienna Convention on the Law of Treaties protects against retroactivity of ‘Brexit’

The 1969 Vienna Convention on the Law of Treaties (‘the Convention’) is the international legal framework within which the exit of the United Kingdom from the European Union takes place. Brexit is not an exception to the rule that the Convention enshrines: termination of or withdrawal from treaty have prospective effects only and any retroactive effect on ongoing positions is to be prevented. The article makes three arguments. First, Art. 70(1)(b) of the Convention reflects customary international law. Second, Art. 70 of the Convention protects rights, obligations and legal situations, and the interpretation of the provision in the context of its drafting history underlines that this includes the rights of individuals that were created in the execution of the treaty. Third, Art. 70 of the Convention governs next to Art. 50 TEU the exit of a State from the European Union. Financial obligations and citizenship rights within the meaning of Art. 70(1)(b) of the Convention were created in the execution of the Treaties by all Member States, and these continue after Brexit. A related argument concerns the judicial enforceability of the Convention. The conclusions outline the implications for a holistic conceptualisation of an EU legal order within international law and for the law of complex international organisations.