The Supreme Court rules that Parliamentary approval is required to invoke Article 50 of the Treaty on European Union: A Note on the Supreme Court's judgment in R (Miller) v Secretary of State for Exiting the EU

By Richard Eccles, Cathal Flynn


On 24 January 2016, the UK's Supreme Court issued its judgment on the government's appeal against the High Court's ruling in R (Miller) v Secretary of State for Exiting the EU.  The Supreme Court decided by a majority of 8 to 3 to dismiss the government's appeal and to uphold the High Court's ruling that giving notice of the UK's withdrawal from the EU under Article 50 of the Treaty on the EU ("TEU") requires the authorisation of Parliament as a whole and cannot be done by the executive or by ministers acting under Royal prerogative.  Our note on the High Court's judgment of 3 November 2016, which explained the principles of Parliamentary sovereignty and Royal or Crown prerogative that are key to the Supreme Court proceedings, is available here

The judgment of the majority of the Supreme Court decisively upheld the fundamental constitutional principle that legislation, adopted by Parliament as a whole, is necessary to authorise the giving of a notice under Article 50 because such a notice will directly lead to the EU Treaties and much EU law ceasing to have effect in the UK. The European Communities Act 1972 ("ECA 1972") gave domestic effect to EU law including EU law rights granted to individuals. The Supreme Court went further than the High Court by indicating clearly, rather than by implication, that legislation will be needed to authorise the use of Article 50.

The main issue

The government argued that the ministers can exercise Royal prerogative in relation to the UK's participation in international treaties so as to be able to give a notice under Article 50 without involving Parliament. However, as Article 50 itself states, a notice of withdrawal from the EU can only be given by a member state in accordance with its own constitutional requirements. The Supreme Court, like the High Court previously, held that it is a fundamental principle of the UK constitution that, unless primary legislation expressly permits it, the Royal prerogative does not enable ministers to change statute law or common law. This principle dates back to the early 17th century and the Case of Proclamations (1610) and the Supreme Court (like the High Court) quoted Sir Edward Coke CJ's judgment in that case.

The Supreme Court referred to the unique and unprecedented character of the ECA 1972 in establishing a mechanism that gave effect in domestic UK law to the provisions of the EU Treaties. By contrast, normally international treaties are binding only in international law and not as part of UK law. By virtue of the ECA 1972, EU law became a source of UK law and also took precedence over all domestic sources of UK law. However, as the Supreme Court stated, this "unprecedented state of affairs" could only continue for so long as Parliament wished it to do so, and the ECA 1972 could be repealed, but only by statute and not by ministerial act. 

The Supreme Court rejected the Government's argument that, because it allowed for a dynamic process by which changes in EU law are also brought into domestic law, the ECA 1972 "effectively" provided for the UK's withdrawal from the EU Treaties. The Court underlined the vital difference between changes in UK law resulting from variations in the content of EU law and changes resulting from withdrawal from the EU. According to the Court, the latter would make a fundamental change to the UK's constitutional arrangements. That would require Parliamentary authorisation.

It was stated to be common ground that because the EU Treaties apply in UK law, UK domestic law will change as a result of the UK ceasing to be a party to the EU Treaties, which will be the direct result of the giving of an Article 50 notice. Upon the UK's withdrawal from the EU, EU law will cease to be a source of domestic law for the future. Therefore the rights enjoyed by UK residents under EU law will be affected by the Article 50 notice. Such a major change must be effected in the only way that the UK constitution recognises, namely by Parliamentary legislation.

The judgment of the Supreme Court differed from the High Court judgment in stating that it was common ground that an Article 50 notice cannot be withdrawn once given. The Supreme Court therefore proceeded on this basis without expressing any view as to whether such a notice could or could not validly be withdrawn. The point is significant because there was a possible argument following the High Court judgment, that if an Article 50 notice is revocable, the giving of such notice would not necessarily lead to repeal or changes in the domestic law that resulted from the incorporation of EU law into UK law under the ECA 1972. However, the Supreme Court accepted the argument that when the notice is given, the UK would have embarked on an irreversible course that will lead to the EU Treaties and much of EU law ceasing to have effect in the UK, whether or not Parliament repeals the ECA 1972. The fact that new legislation is anticipated in connection with the UK's eventual withdrawal, to repeal the ECA 1972, does not change the position. The Supreme Court stated that if ministers give notice under Article 50 without prior Parliamentary authorisation, "… the bullet will have left the gun before Parliament has accorded the necessary leave for the trigger to be pulled". The Supreme Court added "The very fact that Parliament will have to pass legislation once the Notice is served and hits the target highlights the point that the giving of the Notice will change domestic law: otherwise there would be no need for new legislation."

Referendum issues

The position was not affected by the EU Referendum Act 2015 or the result of the EU Referendum held on 23 June 2016, because the Act did not itself provide for any legislative change to implement the result of the referendum. The referendum result had only political, not legal force. The Referendum did not itself change the law so as to allow ministers to withdraw the UK from the EU without legislation. The essential point is that if what would otherwise be an act of Royal prerogative would result in a change in domestic law, the act can only lawfully be carried by means of primary legislation. 

Devolution issues

The Supreme Court decided unanimously that the devolution Acts had no effect on the process of a UK withdrawal from the EU. The devolved institutions do not have a veto on a decision by the UK Parliament to leave the EU. The Supreme Court acknowledged the importance of the Sewel Convention concerning relationships between the UK Parliament and the devolved legislatures, but stated that the policing of its scope and operation is outside the constitutional remit of the judiciary. 


It is now clear that the UK government must obtain the approval of Parliament as a whole, and moreover must pass legislation, before invoking Article 50 TEU.  This risks delaying the government's plans to trigger Article 50 by the end of March 2017, but the government is understood to have already started preparations for the necessary Bill.

If, as anticipated, the Bill is short and tightly drafted, there may be only limited scope for tabling amendments, but it remains to be seen what amendments, if any, may be made to such a Bill, in the House of Commons and also the House of Lords. Indeed the overall position of the House of Lords is not a foregone conclusion.  

The Supreme Court's judgment is of huge significance in confirming the sovereignty of Parliament in relation to all changes to domestic law. In relation to the Brexit process, whether or not the judgment affects the final outcome, it will give increased scope for Parliament to become more involved at an early stage.

For further information please contact the authors. 

This article is part of our Brexit series.



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