Supreme Court Judgment: Article 50 Bulletin

Brexit: Supreme Court holds that an Act of Parliament is necessary before UK Government can trigger Article 50


The UK Supreme Court today held by a margin of 8 judges to 3 that the UK Government cannot trigger the UK's exit from the European Union without an Act of Parliament. It also held unanimously that UK ministers were not legally compelled to consult the devolved legislatures before triggering Article 50.

What is the case about?

In June 2016, the UK voted to leave the EU. This case has been about the process for doing so.

Article 50 of the Treaty on European Union sets out the exit procedure. Article 50(1) states that any Member State may decide to withdraw from the EU in accordance with its own "constitutional requirements". The question of what the UK's constitutional requirements are for these purposes was the key issue in the case. The UK Government took the view that it could trigger Article 50 without going through the UK Parliament. A number of different parties disagreed.

Judicial review proceedings were brought to decide the point. At first instance, the English High Court held that Article 50 could not be triggered by the UK Government without Parliamentary approval. The UK Government appealed. The appeal was heard in the Supreme Court in December by a panel comprising (for the first time in its history) all eleven Supreme Court judges.

Who are the parties?

The Lead Claimant is business-woman Gina Miller. A number of other parties also intervened in the High Court, on the basis that their rights would be affected by Brexit in various different ways.

Further parties intervened or were otherwise involved at the Supreme Court level, including: the Lord Advocate in Scotland; the Counsel General for Wales; the Attorney General for Northern Ireland; a group of expats; the Independent Workers Union; and Lawyers for Britain.

The UK Government was represented by the Secretary of State for Exiting the European Union.

The key arguments

The UK Government argued that the long-established principle of "Royal prerogative" allowed it to act without Parliament in matters relating to the conduct of international relations and the making and unmaking of treaties on behalf of the UK. This principle extended to exiting the EU.

The Lead Claimant argued that prerogative powers could not be exercised where this would frustrate or undermine rights and duties established by Acts of Parliament.

Other issues raised included: parliamentary sovereignty; devolution and related issues of constitutional law (see further below); EU citizenship rights generally; the rights of British citizens who exercise their right to free movement by living elsewhere in the EU; and the rights of children and their carers whose immigration status in the UK might be affected by Brexit.

The Supreme Court has held that the UK Government cannot trigger Article 50 without an Act of Parliament. This is on the basis that whilst Government does have prerogative power to withdraw from international treaties, it cannot exercise such power without an Act of Parliament if it would, in doing so, change UK laws. Where the EU makes new laws, those laws become part of UK law. EU law is therefore an independent source of UK law until Parliament decides otherwise. Withdrawal from the EU treaties will cut off a source of UK law, and the Government cannot therefore trigger the UK's exit without authorization from Parliament.

What arguments did the devolved governments raise?

The Scottish Government had two main arguments.

The first related to the central question of whether the UK Government could use the royal prerogative to make an Article 50 notice without an Act of Parliament. On this point, Scotland's Lord Advocate agreed with the position of the Lead Claimant but relied on different sources, including the Claim of Right Act passed by the old Scottish Parliament in 1689 and the Acts of Union 1706 and 1707.

The second related to the operation of what is commonly referred to as the Sewel Convention - the constitutional convention that the UK Parliament will not normally legislate with regard to devolved matters without the consent of the Scottish Parliament. A recent amendment to the Scotland Act 1998 now enshrines a similar principle in Section 28(8) which requires a legislative consent motion to be passed by the Scottish Parliament where the UK Parliament is to legislate on devolved matters. Although the triggering of Article 50 of itself is not a devolved matter, the Lord Advocate argued that the withdrawal of the UK from the EU would alter the competence of the Scottish Parliament and Government and the law applicable in Scotland within devolved competence, and therefore the Scottish Parliament's consent should be sought.

The Welsh Government's and Northern Irish applicants' arguments mirrored the Scottish Government's position, although with different source authority. In the case of Northern Ireland, the applicants (including a group of members of the Northern Irish Assembly and a victims' campaigner) also argued that, prior to the triggering of article 50, the Northern Ireland Office was required to undertake an assessment of the impact of this step on the promotion of equality for people in Northern Ireland.

The UK Government argued that the conduct of foreign affairs was a reserved matter for the purposes of the devolution legislation, such that the devolved legislatures did not have competence over it. In relation to the Sewel Convention, the UK Government submitted that it was not relevant as there was no Bill before the Westminster Parliament.

The Supreme Court held unanimously that UK ministers are not legally compelled to consult the devolved legislatures or seek their consent before triggering Article 50. This is on the basis that relations with the EU are a matter for the UK Government.

Why does this matter?

The Government is said to have prepared various versions of a draft Bill ready to be introduced within the next week depending upon the Supreme Court ruling. Whether its anticipated brevity and simplicity will help curtail debate and scope for amendment in both the House of Commons and the House of Lords - essential if it is to achieve its ambitious timetable of triggering Article 50 by the end of March - remains a major challenge. Managing the House of Lords in particular in this process may prove difficult.

The standard procedure for creating a new law will presumably still have to be followed. Following the drafting of the Bill itself, this comprises a number of readings in the House of Commons, along with detailed examination of the Bill by committee and a reporting stage. After the final reading, Members of Parliament vote on whether the Bill should be approved. A similar process is then followed in the House of Lords. Once passed, a Bill needs to receive Royal Assent before it becomes an Act of Parliament. The process may well provide another airing of the arguments for and against leaving the EU in both the House of Commons and the House of Lords. The outcome of the vote on the Bill is also potentially unpredictable. Most MPs are thought to have voted for the UK to stay in the EU. That said, it will be difficult for Parliament to ignore the referendum result, and in a House of Commons debate in December, MPs approved in principle the UK Government's timetable for triggering Article 50.

The decision by the Supreme Court that there is no place for the devolved legislatures in the Article 50 trigger does remove a significant obstacle from the path of the Government.

What other legal cases are in the offing?

A pro-Europe think-tank (joined by other claimants) is arguing that Britain's exit from the EU should not be taken to mean an exit from the EEA. They say that Article 127 of the EEA Agreement, to which the UK is a contracting party, specifies a separate departure process from the one set out in Treaty on European Union.

A group in Ireland is also planning to litigate the question of whether an Article 50 notice, once given, can be revoked. In the Article 50 proceedings, the UK Government appeared to concede that the notice was not revocable. In legal terms however, this is still an open question on which there are different views. The Court of Justice of the European Union could be the final court of reference for such a case. This case also seeks to refer the question of whether Brexit means the UK also leaves the European Economic Area (EEA).


For constitutional lawyers, this case has been a rare opportunity to explore sometimes complex legal arguments about the inter-twined roles of the UK Government and Parliament. For most people, though, the outcome is the most important thing. For now, it looks like there is a lot of work to be done between now and March if the proposed trigger date is to hold good. But there has been significant progress outside the law courts in recent days, in the form of May's speech setting out twelve objectives for Brexit and laying the groundwork for the exit negotiations.

We are also likely to see further litigation, both in the UK and beyond, relating to the Brexit process. This much is clear - so far exiting the EU is proving far from straightforward.