In brief…

This morning the Supreme Court upheld the High Court’s judgement in R (on the application of Miller and others) v Secretary of State for the Exiting of the EU [2016] EWHC 2768 (Admin) by a majority of 8 to 3. The Government cannot, therefore, use prerogative powers to give notice under Article 50 of the Lisbon Treaty in order to withdraw the UK from the EU; such notice will first require an Act of Parliament. This decision follows the Government’s appeal from the High Court’s judgement in November 2016, which held that the UK constitution requires the approval of Parliament before the Government can begin the formal process of leaving the EU.

While it remains to be seen what will be set out in the necessary Act of Parliament, what is clear today is that whether or not Brexit will go ahead following last June’s referendum will be the subject of debate and approval by Parliament.

Whose decision is it anyway?

Legislature v Executive

Article 50(1) provides that ‘any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements’. The High Court had held that our constitutional requirements include an Act of Parliament to authorise the Government to give notice under this Article; the Crown does not have the necessary prerogative power to give such notice because the European Communities Act 1972 (the “1972 Act”) gives rights to individuals which cannot be taken away without Parliamentary approval to do so.

In appealing that decision (and among numerous arguments), the Government sought to rely on the established position that the conduct of international relations and the making and withdrawing from treaties are within the scope of the Crown’s prerogative powers and are not limited by the 1972 Act and, therefore, this power could be used to invoke Article 50.

It was held by the Supreme Court that section 2 of the 1972 Act authorises a dynamic process by which EU law becomes a source of UK law and takes precedence over all domestic sources of UK law, including statutes. So long as the 1972 Act remains in force its effect is to constitute EU law as an independent and overriding source of domestic law.

The Supreme Court found that the Government’s arguments were inconsistent with the principle of the sovereignty of Parliament, as it was held that the Crown cannot change domestic law through the exercise of its prerogative powers. The fact that withdrawal from the EU would fundamentally change the UK constitution and would remove some existing domestic rights of UK residents renders it impermissible for the Government to withdraw from the EU Treaties without prior Parliamentary authority. Clear words could have been included in the 1972 Act to permit the use of prerogative power but they were not so included.

Equally, the European Union Referendum Act 2015 could have specified the consequences of a particular outcome – the effect of a referendum must depend on the terms of the statute that authorises it. It did not. It was silent, unlike the Acts authorising other referenda in the past. Therefore, the outcome of last June’s EU referendum is of political, but not legal, significance.

Westminster v Devolved Legislatures

References from Northern Ireland, and interventions by the Lord Advocate for the Scottish Government and the Counsel General for Wales for the Welsh Government, raised the 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 given under Article 50 or otherwise operate to restrict the Government’s power to withdraw from the EU.

The Supreme Court unanimously concluded that relations with the EU and other foreign affairs are reserved to Westminster, not to the devolved Scottish parliament, Welsh Assembly or Northern Ireland.

The Supreme Court concluded that neither Scotland, Wales or Northern Ireland have a veto on the UK’s decision to withdraw from the EU - legislative consent of all three devolved parliaments is not needed before triggering Article 50, despite withdrawal from the EU altering the competence of the devolved institutions and removing responsibilities to comply with EU law. The Court considered that the Sewel Convention – in connection with which the UK Parliament will not usually exercise its right to legislate in relation to devolved matters without agreement of the devolved legislature(s) - operates as a political rather than legal constraint on the activity of the UK Parliament. Its scope and operation is not within the remit of the courts.


Today, a clear dividing line was drawn between law and politics.

Important constitutional concepts have been upheld: the rule of law, the separation of powers and the sovereignty of Parliament – the latter being one of the Leavers’ key campaign issues last summer. Simply put, the will of the democratically-elected UK Parliament – in the absence of clear words to the contrary – is supreme and cannot be displaced through the use of prerogative or devolved powers.

We are yet to see what form the Brexit bill might take. The MPs and Lords will have the opportunity to hold the Government to account and could potentially use this opportunity to include obligations to consult Parliament on any deal which is negotiated as part of the UK’s withdrawal from the EU.

There is a very tight time frame in which to obtain Royal Assent and bring a Brexit Act into force if the Prime Minister is to trigger Article 50 by the end of March 2017, as has previously been suggested.

We will prepare further updates as we learn more about the Brexit bill and what it will mean for the UK’s negotiations to exit the EU.

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Joanna Howard


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Claire Whittle

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Posted on 24/01/2017 in Brexit Briefcase

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