Theresa May must consult Parliament in order to trigger Article 50, the Supreme Court has ruled.

Here is a summary of their ruling:

Background to the appeals

Article 50 of the Treaty on the European Union provides, in summary terms, that, if a member state decides to withdraw from the European Union (“the EU”) ‘in accordance with its own constitutional requirements’, it should serve a notice of that intention (“a Notice”), and that the treaties which govern the EU (“the EU Treaties”) “shall cease to apply” to that member state within two years thereafter. Following the June 2016 referendum, the Government proposes to use its prerogative powers to withdraw from the EU by serving a Notice withdrawing the UK from the EU Treaties.

The principal issue in these appeals is whether such a Notice can, under the UK’s constitutional arrangements, lawfully be given by Government ministers without prior authorisation by an Act of Parliament. References from Northern Ireland, and interventions by the Lord Advocate for the Scottish Government and the Counsel General for Wales for the Welsh Government, raise the additional issues of whether the terms on which powers have been statutorily devolved require consultation with or the agreement of the devolved legislatures before Notice is served, or otherwise operate to restrict the Government’s power to do so (‘the devolution issues’).

The UK’s constitutional requirements are a matter of domestic law which the parties all agree should be determined by UK judges. The issues in these proceedings have nothing to do with political issues such as the merits of the decision to withdraw, the timetable and terms of so doing, or the details of any future relationship between the UK and the EU.

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The claimants submit that, owing to the well-established rule that prerogative powers may not extend to acts which result in a change to UK domestic law, and withdrawal from the EU Treaties would change domestic law, the Government cannot serve a Notice unless first authorised to do so by an Act of Parliament. Resolution of this dispute depends on the proper interpretation of the European Communities Act 1972 (‘the ECA’), which gave domestic effect to the UK’s obligations under the then existing EU Treaties, together with subsequent statutes, which gave effect to and related to later EU Treaties, and the European Union Referendum Act 2015.

The devolution issues require the court to consider whether the terms of the Northern Ireland Act 1998 (‘NIA’), and associated agreements, require primary legislation, and the consent of the Northern Ireland Assembly and/or the people of Northern Ireland, before a Notice can be served. Under each of the devolution settlements in Northern Ireland, Scotland and Wales the devolved legislatures have responsibilities to comply with EU law, and there is a convention (‘the Sewel Convention’) that the UK Parliament will not normally exercise its right to legislate with regard to devolved matters without the agreement of the devolved legislature.

Supreme Court Brexit Challenge Show all 13 1 /13 Supreme Court Brexit Challenge Supreme Court Brexit Challenge People wait to enter the public gallery outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge Gina Miller, co-founder of investment fund SCM Private arrives at the Supreme court in London on the first day of a four-day hearing Getty Supreme Court Brexit Challenge A man waves the EU flag in front of the Supreme Court Getty Supreme Court Brexit Challenge Satirical artist Kaya Mar poses with two of his paintings in front of the Supreme Court Getty Supreme Court Brexit Challenge Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin. The eleven Supreme Court Justices will hear the government's appeal, following the High Court's recent decision that only Parliament can trigger Article 50 Getty Supreme Court Brexit Challenge The eleven Supreme Court Justices will hear the government's appeal, following the High Court's recent decision that only Parliament can trigger Article 50 Getty Supreme Court Brexit Challenge Businesswoman Gina Miller arrives at the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin Getty Supreme Court Brexit Challenge Attorney General Jeremy Wright arrives at the Supreme Court in London EPA Supreme Court Brexit Challenge Protesters outside the Supreme Court in London, where the Government is appealing against a ruling that the Prime Minister must seek MPs' approval to trigger the process of taking Britain out of the European Union PA wire Supreme Court Brexit Challenge A protesters wearing a judge's wigs and robes stands outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge A protester holds up a placard outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court Getty Supreme Court Brexit Challenge A man waiting to enter the public gallery waves a European Union flag outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters

The principal issue was raised in proceedings brought by Gina Miller and Deir Dos Santos against the Secretary of State for Exiting the European Union. The Divisional Court of England and Wales (Lord Thomas LCJ, Sir Terence Etherton MR and Sales LJ), declared that the Secretary of State did not have power to give Notice, without Parliament’s prior authority. The Secretary of State has appealed to the Supreme Court against this decision. The Northern Ireland claims were heard together by Maguire J in the Northern Ireland High Court, who determined and dismissed the devolution issues, and, on an application by the Attorney General for Northern Ireland Maguire J referred four issues to the Supreme Court and the Northern Ireland Court of Appeal referred one further issue.

Judgement

The Supreme Court by a majority of 8 to 3 dismisses the Secretary of State’s appeal (Lord Neuberger, Lady Hale, Lord Mance, Lord Kerr, Lord Clarke, Lord Wilson, Lord Sumption and Lord Hodge in the majority with Lord Reed, Lord Carnwath and Lord Hughes dissenting). In a joint judgment of the majority, the Supreme Court holds that an Act of Parliament is required to authorise ministers to give Notice of the decision of the UK to withdraw from the European Union. Each of the dissenting justices gives a separate judgment.