On 24 January, the Supreme Court decided, by a majority of eight judges to three, that the Government can only trigger Article 50 – the process by which the UK can leave the EU – after an Act of Parliament has been passed. Nothing less will do. 

This ruling made constitutional history and clarified the extent of the powers of the executive - in this case, the Prime Minister of the United Kingdom, Theresa May, and of the UK Parliament.

There was, and remains, a common misconception that this case set out to defy the referendum result and, ultimately, to stop or delay Brexit. Put plainly, it did not. What the aftermath of the referendum revealed was a staggering lack of clarity around the legal procedure to be followed under the UK’s constitutional requirements (per Article 50(1) of the Lisbon Treaty) when leaving the EU. Ultimately, to get clarity this case had to go right to the heart of the application of the constitutional principles of the separation of powers, parliamentary sovereignty, the independence of the judiciary and the rule of law. This has been a necessary process to ensure that the UK leaves lawfully, securing legal certainty, before rather than after the event.

The question at the centre of the case concerned whether the Government can remove a source of domestic constitutional law and/or domestic rights granted by an Act of Parliament and arising under the EU Treaty. This was set against a constitutional backdrop in which Parliament is sovereign as regards the making of laws (other than the common law), but subject to the rule of law as enforced by the courts. The electorate is sovereign politically. Parliamentary sovereignty as regards domestic laws means that we must have a dualist constitution: only Parliament can give effect to international treaty rights/obligations in domestic law, as opposed to international rights/obligations as between states under international law.

The key arguments of the lead claimant, Gina Miller, represented by Mishcon de Reya, took the judges back to cases and statutes in the seventeenth century, including the Bill of Rights, which demonstrated that Parliament is sovereign as law-maker. The residual Royal Prerogative powers of the Government - regarding international relations, and treaties in particular - exist solely in relation to international law rights/obligations. EU rights and obligations are made domestic law by virtue of the European Communities Act 1972 (ECA).  Once the Government triggered Article 50, the Notice would be irrevocable, and there would therefore inevitably be a loss of at least some rights in domestic law under the ECA. Therefore, only Parliament can grant such a power, and it requires an Act of Parliament to do so.

The Supreme Court agreed with Gina Miller’s case and noted that the Government’s case would lead to perverse results; if correct, it meant that the Government could always have withdrawn the UK from the EU without reference to Parliament. It could do so even if there was a referendum result in favour of remaining in the EU.

As a result, the Government published The European Union (Notification of Withdrawal) Bill to gain Parliament’s permission to start the Brexit process without conditions as to the negotiation strategy and objectives. The aim is that this will be achieved well ahead of the stated deadline of 31 March 2017.

It remains to be seen whether the Bill will be amended by the UK Parliament to fetter the Government’s discretion and/or impose requirements for Parliamentary security of the process. Furthermore, there is an application in the English court in relation to withdrawal from the EEA under Article 127 of the EEA and one concerning the revocability of the Article 50 Notice in the Irish court (seeking a referral to the CJEU).

Among the lessons to be learned are that there is considerable ignorance as to the fundamental principles of our constitution, as regards the nature of representative parliamentary sovereignty, the role of referendums and the role of the court in upholding the rule of law. This is a real weakness in our system which needs to be corrected. On a positive note, the courts managed the whole process in under seven months, a clear indication of the efficiency of our judicial system which has been noticed both nationally and internationally. And, last but not least, any future referendum will no doubt spell out what, if any, the legal consequences of the result will be.

Rob Murray is a partner in Mishcon De Reya’s Dispute Resolution department. He specialises in competition law damages claims and has represented clients in leading competition damages claims in the English High Court and the Competition Appeal Tribunal. Rob is ranked as a Leading Individual for Competition Litigation in Legal 500 2015 and Chambers & Partners 2016. Rob is also Council Member of the European Maritime Law Organisation and a member of the Steering Committee of the European Competition Litigation Forum. He is also a former Reporting Panel member of the UK Competition Commission.