Today, by a majority of 8:3, the UK Supreme Court confirmed that an Act of Parliament is necessary before the UK can serve notice of its intention to leave the EU pursuant to Article 50 of the Treaty on European Union "TEU". The rights that the EU has conferred on UK citizens played a pivotal role in the judgment.

The Supreme Court judgment follows the decision of the High Court in R(Miller) v Secretary of State for Exiting the EU on 3 November 2016 in which the applicants were successful and which was subsequently appealed by the UK government.

Article 50 requirements and the Royal Prerogative

Article 50 of the TEU provides that where a Member State decides to withdraw from the European Union ("the EU"), it must do so "in accordance with its own constitutional requirements". Following the June Referendum, the key question became whether an Article 50 notice of the UK's intention to withdraw from the EU would be in accordance with the constitutional requirements of the UK if the Cabinet exercised the Royal Prerogative to the exclusion of an Act of Parliament.

Changing domestic law requires an Act of Parliament

It is an established principle of the British constitution that an Act of Parliament can only be repealed by a subsequent Act of Parliament. In relation to the European Communities Act, 1972 ("ECA") this means not simply by a subsequent Act of Parliament that is in conflict with it, but by a subsequent Act that repeals it. The Court held that through Section 2 of the ECA, European law has become a source of United Kingdom law and takes precedence over all domestic sources of domestic law. Withdrawal from the EU is a fundamental change to the United Kingdom's constitutional arrangements, by cutting off a source of European Law. Such a change needs to be effected by Parliamentary legislation.

Removal of United Kingdom citizens' and residents' rights and treaty obligations

It also noted that the UK's withdrawal from the EU would remove some rights from citizens and residents of the United Kingdom. Parliamentary authority is thus needed to withdraw from the EU treaties. In the Court's view it would thus be unconstitutional for the Government to serve notice to withdraw without the prior authority of Parliament. The judgment notes that had Parliament intended the Government to be able to withdraw from the EU without recourse to Parliament, express language to this effect could have been included in the enacting legislation.1 In the Court's view, the absence of such an express power, the development of ministerial controls in the post 1972 jurisprudence and the words of the ECA itself serve to emphasise that Parliamentary authority is required.

During the course of this morning, the UK Attorney-General has confirmed that the Government will comply with the judgment.

In conclusion, the Court reaffirmed the constitutional sovereignty of Parliament, and the rule of recognition that reflects this doctrine. The change in the law required to implement the Referendum's outcome must be made in the only way permitted by the UK constitution, namely by legislation. The referendum's outcome is a political fact of great significance that must be given effect through an Act of Parliament.

Devolution Issues

A number of devolution arguments had also been referred to the Supreme Court by the Attorney General for Northern Ireland and the Northern Ireland Court of Appeal and were addressed in this morning's judgments and press conference. These related primarily to the devolution Acts2 passed by the UK Parliament and whether the devolved legislatures of Northern Ireland and Scotland had a veto on the UK's decision to withdraw from the EU.

The Court held that relations with the EU and other matters relating to foreign affairs are reserved to the UK Government and Parliament and that withdrawal from the EU was not a function given to the Secretary of State for Northern Ireland under the Northern Ireland Act 1998. Accordingly, no veto is afforded to the devolved assemblies in relation to serving an Article 50 notice. In her statement on the case, Nicola Sturgeon has already suggested that the case raises "fundamental issues" for Scotland and that "the Scottish Government will bring forward a Legislative Consent Motion and ensure that the Scottish Parliament has the opportunity to vote on whether or not it consents to the triggering of Article 50."

What next?

The UK Government will have to obtain the approval of Parliament before serving notice of its intention to withdraw from the EU. It will seek to do so by proposing a new Act of Parliament which will have to be approved by both the House of Commons and the House of Lords. David Davis, the UK's Brexit Secretary has stated today that an Article 50 Bill will be introduced "within days".