On 4th December 2018 the Advocate General of the European Court of Justice published his Opinion on whether the UK may unilaterally revoke the Article 50 TEU notification of intention to withdraw, followed on 10th December by the decision of the Court. While the Advocate General concluded that the UK can stop Brexit until the Article 50 notification has resulted in the UK’s formal withdrawal, i.e. 29 March 2019, the Court went further in ruling that Brexit can be stopped until a withdrawal agreement has entered into force or, if no agreement, for as long as the two-year period provided for in Article 50(3), possibly extended, has not expired.

In his Opinion, the Advocate General cites Professor Paul Craig’s ‘Brexit: A Drama in Six Acts’ (2016) 41 European Law Review 447, Sir Jeremy Lever’s co-authored ‘In the matter of Article 50 of the Treaty on European Union’ (‘The Three Knights’ Opinion’) 2017, and Antonios Tzanakopoulos's analysis on Article 68 of the Vienna Convention on the Law of Treaties (found here on SSRN) on revocation of notifications of withdrawal from treaties.