UK Supreme Court Rules That An Act Of Parliament Is Required To Trigger Withdrawal From The European Union

In a highly significant judgment of constitutional and political importance, the UK Supreme Court confirmed yesterday that the initiation of the UK's withdrawal from the European Union (the "EU") will require a prior Act of Parliament.1 The Supreme Court's decision, by a majority of eight to three, sets the stage for considerable further debate in Parliament, at the very least in the period leading up to the end of March 2017, by which time it is the Government's stated aim to invoke Article 50 of the Treaty on the European Union ("Article 50").

THE PRINCIPAL ISSUE: THE POWER TO TRIGGER ARTICLE 50

In the referendum held on 23 June 2016, the majority of UK voters voted in favour of leaving the EU. Under Article 50, a member state may decide to withdraw from the EU "in accordance with its own constitutional requirements" and is then required to give notice to the European Council of that decision.2 Thereafter, the treaties governing the EU will cease to apply to that member state either from the date on which any withdrawal agreement comes into force or, failing that, after two years from the date of the notice.3

The Government had argued (and maintained on appeal) that it was entitled to invoke Article 50 under the Crown's prerogative powers (i.e., without the authorisation of Parliament), given that the making of, and withdrawal from, international treaties (and the conduct of foreign affairs in general), has traditionally fallen within the scope of prerogative powers.

This argument had failed at first instance before a Divisional Court of the...