Article 50 (1) of the Treaty of the European Union states that “Any member state may decide to withdraw from the Union in accordance with its own constitutional requirements.” The Supreme Court in Miller was asked the narrow legal question of whether the government has the power to give notice to withdraw without Parliamentary legislation. The majority of 6 found that it would be “[i]nconsistent with longstanding and fundamental principle for such a far-reaching change to United Kingdom constitutional arrangements to be brought about by ministerial decision and action alone” [81]. Lord Reed, in the minority, disagreed about how far-reaching that change would be, arguing that “although no-one can doubt the importance of EU law, the effect given to it by the 1972 Act has not altered any fundamental constitutional principle in respect of the identification of sources of law” [228]. For him the 1972 Act is an empty vessel, the operation of which is conditional on the application of the EU treaties to the UK. Thus he sees no difference between changes to domestic law resulting from the ordinary variations in EU law and changes resulting from the withdrawal by the UK from the European Union. The result is ironic. Lord Reed takes a more Parliamentary sovereigntist (dualist) account of the status of EU law as part of the law of the United Kingdom. This leads to his dissenting conclusion that Parliamentary legislation is not required for notification of withdrawal. Parliamentary sovereignty is at the core of the United Kingdom constitution under either view.

Even if one prefers the minority approach, that does not necessarily have a bearing on the question of whether Parliamentary authorisation should (as opposed to must) be sought. The Supreme Court provides answers about what powers Ministers have, but only just begins to address the larger question of what are the United Kingdom’s constitutional requirements for such a change.  After all, if it were merely a question of power then it is the Queen who actually has it – but the fact that it is the responsible government who advises the Queen to act is no less a requirement of the constitution. Britain’s political constitutional tradition has never simply been about having the power in a legal sense. The key limits on exercises of power involve the mutual self-restraint and proper conduct of political actors enforced by politics and convention. All of the Court agreed with the standard view that constitutional conventions are not matters which courts should enforce. But there was also a clear recognition that the conventional constitution includes matters such as the relationship between the United Kingdom and the devolved Parliaments of Scotland, Northern Ireland and Wales.  Politicians must now turn to address these and the other broader constitutional requirements in order to tend to and preserve British traditional values of which they profess to be so fond. Members of Parliament should take courage from this judgment to take their political responsibilities in a representative democracy seriously (see Jeff King’s blog at J. King, ‘What Next? Legislative Authority for Triggering Article 50’ U.K. Const. L. Blog (8th Nov 2016).

Janet McLean is Professor of Law at The University of Auckland.

Click here for further analysis of the Supreme Court’s Miller judgment.