Today the UK Supreme Court has ruled that the UK Government does not have the power to trigger Article 50 without first being authorised to do so by an Act of Parliament. The decision in R (on the application of Miller and another) v Secretary of State for Exiting the European Union [2017] UKSC 5 upholds the first-instance decision of the High Court made in November. As in the High Court proceedings, the Supreme Court stressed that its decision addresses questions of law only, and makes no comment on the merits of leaving the EU, which it holds to be a purely political issue. All 11 Supreme Court judges sat to hear the appeal, a first in the history of the Supreme Court and which demonstrates the significance of the case.

The Supreme Court considered whether, as a matter of constitutional law, the Government is entitled to use its treaty-making powers under the Royal Prerogative to trigger Article 50. The “Royal Prerogative” is a body of discretionary powers held by the Crown and exercised by Government in carrying out executive functions. The exercise of prerogative power does not require prior parliamentary approval. At the initial hearing, the High Court found that the Government was not entitled to use such powers to trigger Article 50. This High Court decision rested on the constitutional principle of Parliamentary sovereignty, which provides that Parliament is supreme and no person or body can override, nullify or set aside legislation enacted by Parliament, other than Parliament itself.

Act of Parliament required

A majority of 8 to 3 of the Supreme Court judges held that an Act of Parliament will be required before the UK can trigger Article 50. While the European Communities Act 1972 remains in force, EU law constitutes an independent and overriding source of domestic law. As such, withdrawing from the EU will inevitably change domestic law by removing this source of law, effecting a significant constitutional change. The Court found that it would be “inconsistent with long-standing and fundamental principle” for this fundamental change to be brought about by Government acting under prerogative power without reference to Parliament, especially in light of the fact that this source of law was brought into existence by Parliament through primary legislation. Furthermore, as withdrawal from the EU will remove certain existing domestic law rights from UK citizens, the need for legislation is reinforced.

While the Court held that primary legislation will be required, the Court stated that the form that such legislation should take is entirely a matter for Parliament. It noted that it could be a “very brief statute“, as there is “no equivalence between the constitutional importance of a statute…and its length or complexity“.

Devolved matters

In addition to receiving submissions from the original parties to the proceedings, the Court heard arguments from the devolved Scottish and Welsh Governments, and individuals appealing the decision of the High Court of Northern Ireland, as to whether Parliament required the consent of the devolved legislatures before authorising the Government to trigger Article 50. On this question the Court unanimously found that consent from the devolved legislatures is not required before the relevant Parliamentary legislation is enacted. Matters concerning the EU and other foreign affairs are reserved for the UK Government and Parliament, not the devolved administrations.

The devolved parties had stressed the importance of the Sewel Convention, which provides that the UK Parliament will not usually legislate on devolved matters without the consent of the devolved Parliaments, and had argued that that convention required the devolved parliaments’ consent to triggering Article 50. While the Court appreciated the importance of this convention, it maintained that it was a “political restriction on the activity of the UK Parliament“, and that, as with any constitutional convention, it is not the Court’s role to adjudicate on its operation.

What next?

The Prime Minister has stated that notification under Article 50 will be given before the end of March 2017. The Supreme Court’s judgment may delay this timetable unless legislation is passed relatively quickly. While it is thought that the Government has prepared a draft bill already, the wording of this bill is likely to be scrutinised, debated and amended by Parliament before being passed, which may take some time. What’s more, further legal challenges are afoot in the form of judicial review proceedings to address whether withdrawal from the EU will automatically result in the UK leaving the wider European Economic Area (EEA) and the loss of access to the single market. Remaining within the EEA may be seen as a failure by so-called “hard-Brexiteers” as many of the same laws would continue to apply as if the UK had remained a member of the EU.

Once Article 50 is triggered, the UK will have two years to negotiate an agreement with the EU as to its position upon withdrawal, unless the other Member States agree to an extension. The Prime Minister confirmed last week that Parliament will get the opportunity to vote on the final deal agreed with the EU, although it is not clear what form that vote would take. Although the Supreme Court’s judgment has added some certainty to the process of notification, it looks unlikely that the path to “Brexit” will be plain sailing.

The full judgment is available here:

Joanna Ludlam (Partner) and Emma Brown (Trainee Solicitor) of our Dispute Resolution Department acted for the Government of Scotland in both the High Court and Supreme Court proceedings of this case.

To discuss any of the issues involved in this case further, please contact Joanna Ludlam or Francesca Richmond of our Regulatory, Public and Media Law Group.


Joanna Ludlam is a partner in the Dispute Resolution team in the Firm's London office, where she leads the market-leading Regulatory, Public & Media law team in the London office and also co-leads the office's Compliance & Investigations practice group. At an international level, she chairs the Firm's EMEA Compliance & Investigations Group, and is a member of the steering committee of the Global Compliance & Investigations Group.


Francesca Richmond is a partner in the Dispute Resolution team in the Firm's London office, where she advises regulators and regulated entities on advisory, risk management and contentious matters, with a focus on securing commercial outcomes by application of competition law, EU law, human rights and domestic judicial review principles.

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