Unlike breach, withdrawal from an international treaty is in principle a lawful act. Article 54 of the Vienna Convention on the Law of the Treaties allows a State to withdraw from a treaty either in conformity with the relevant provisions or by consent of all parties. In that sense, Article 50 TEU that provides for a Member State ‘to withdraw from the Union in accordance with its own constitutional requirements’ could be seen as a lex specialis to the general international law rule. Helfer has convincingly showed that clauses authorising denunciation and withdrawal from international conventions are far from uncommon.

Having said that, the EU is also a ‘community of unlimited duration, having its own institutions, its own personality, its own legal capacity [and] real powers stemming from a limitation of sovereignty or transfer of powers from the [Member] States’. To the extent that Brexit marks the withdrawal…