Following one of the most constitutionally significant legal challenges in a generation, the Supreme Court today handed down its judgment in the Article 50 Brexit appeal. By a majority of eight to three, the Justices held that the UK could not trigger Article 50 without an Act of Parliament. The Court also ruled that the UK Government was not compelled to consult the devolved institutions or obtain their approval to withdraw.
The Article 50 Brexit case does not concern the merits of the Brexit referendum decision, but rather the mechanism by which withdrawal will be effected. Article 50 of the Treaty of the European Union provides that a Member State can withdraw from the EU, in accordance with its own constitutional requirements, by serving a notice of its intention to do so. In its judgment, the Supreme Court decided the scope and content of those constitutional requirements.
Triggering Article 50 using prerogative powers
The principal issue was whether the Government could give notice under Article 50 using its prerogative powers to enter into and withdraw from international treaties without securing authorisation from Parliament. At first instance, the Divisional Court (Lord Thomas of Cwmgiedd LCJ, Sir Terence Etherton MR and Sales LJ) held that the Government could not.
On appeal, the Respondents argued that it was well-established that prerogative powers could not be used to take measures that would change domestic law. Since giving notice under Article 50 would trigger an irreversible process by which EU law would cease to have effect in the UK, and would alter the rights of UK residents, it could not be done without an Act of Parliament.
The Government in response contended that section 2 of the European Communities Act 1972 (ECA 1972) - by which changes in EU law are brought into domestic law - caters for the use of the prerogative powers for the purpose of Article 50. Since the ECA 1972 gave effect to EU law only to the extent required by the EU Treaties, its effect was contingent upon the UK being an EU member. In addition, the Secretary of State argued that, since legislation following the ECA 1972 had constrained the use of other prerogative powers related to the EU, but not those under Article 50, the latter was not limited by Parliamentary control.
By a majority of 8 to 3, the Supreme Court dismissed the Government’s appeal, holding that an Act of Parliament was required before notice to withdraw from the EU treaties could be given under Article 50. While the Government had powers to enter into international treaties having effect in international law, it could not use those powers to change domestic law. The ECA 1972 gave effect to EU law as an independent source of domestic law. The majority emphasised that changes to domestic law stemming from EU law must be differentiated from changes to domestic law arising from withdrawal. The former are brought into UK law through section 2 of ECA 1972. The latter would unilaterally ‘cut off the source of EU law entirely’ . Such a fundamental change requires Parliament’s approval.
The Supreme Court recognised that Parliament could have given the power to withdraw to ministers under the ECA 1972, but refused to construe the statute in that way in the absence of clear wording. The fact that ministers were accountable to Parliament could not remedy the absence of any initial power to give notice under Article 50, nor would legislation at a later stage at a point when the ‘die will be cast’ suffice .
The fact that Parliament had, since 1972, constrained certain powers of UK ministers at an EU level but had not so constrained the use of Article 50 could not help the Secretary of State where no such power existed in the first place. Overall, since the legislation authorising referendums on EU membership did not specify the legal consequences of a referendum decision, any legal change had to be made through primary legislation.
Three Justices dissented. Lord Reed, with the agreement of Lord Carnwath and Lord Hughes, was of the opinion that the effect of EU law in the UK under the ECA 1972 was ‘inherently conditional’ upon the application of EU Treaties to the UK and upon its membership of the EU. The UK acceded to the Treaties under prerogative powers. Since the ECA 1972 was silent on whether an Act of Parliament was required to trigger Article 50, there was nothing to suggest that the Government’s prerogative powers had been so limited.
Lord Carnwath was also of the view that, while giving notice under Article 50 triggered a political process of negotiations, it did not itself effect such withdrawal. Any change to UK law and the rights of residents was not therefore attributable to the triggering of Article 50. While primary legislation may be required to complete the withdrawal process, it was not in his Lordship’s view required to give the initial notice.
The devolution issues
The Supreme Court also unanimously held that the UK administration is not required to consult the devolved assemblies before Article 50 can be triggered, upholding the decision of the Northern Ireland High Court (Maguire J), below. While the devolution legislation was clearly drafted with UK membership of the EU in mind, it did not require it and relations with the EU remained an issue reserved for the UK institutions.
In addition, while the Northern Ireland Act 1998, section 1, gave Northern Ireland the right to determine its future as part of the UK, it did not require the UK to seek its approval to withdraw from the EU. With regard to the Sewel Convention, while Westminster would not normally legislate on devolved matters without the consent of the devolved authorities, it was not for the Court to police the scope of a constitutional convention.
The full judgment can be read here.
James Eadie QC acts for the Appellant, the Secretary of State for Exiting the European Union.
Lord Keen of Elie QC, Advocate General for Scotland, acts for the Secretary of State for Exiting the European Union.
Christopher McCrudden acts for the Human Rights Consortium, intervening.
 Lord Neuberger (President), Lady Hale (Deputy President), Lord Mance, Lord Kerr, Lord Clarke, Lord Wilson, Lord Sumption and Lord Hodge.