We summarise the High Court’s momentous decision in R (Miller) v. Secretary of State for Exiting the European Union, historically one of the UK’s most significant constitutional cases.


This claim was brought by 2 individuals in order to establish whether or not the Secretary of State could trigger Article 50 of the Lisbon Treaty and hence Brexit without a vote in Parliament.

The Government’s position, and therefore that of the Secretary of State, David Davis, is that he can trigger Brexit under Article 50 unilaterally and without a Parliamentary vote. This, he says, is because the UK constitution effectively gives him prerogative powers to do so. The use of the phrase “prerogative power” has been bandied about a lot in the context of Brexit. Essentially it is an unwritten residual power which the Monarch has to act on their own initiative without any reference to Parliament. Since the 19th century and by convention this has been exercised through the Prime Minister or the Cabinet. One such prerogative power that was not disputed is the prerogative power of the Secretary of State to enter into and withdraw from foreign treaties without reference to Parliament, and the Government relied heavily on this.

The contrary argument – that a majority Parliamentary vote is required before Article 50 is triggered – centred on another fundamental, unwritten, rule of the UK’s constitution; that the Secretary of State cannot use his prerogative powers to override legislation that has been enacted by Parliament, particularly where this would affect citizen’s domestic rights. The case against the government therefore centred on the argument that triggering Article 50 and Brexiting would inevitably have the effect of changing the domestic law in the UK and the rights of citizens, and that this could therefore only happen by means of an act of Parliament.

But what of the prerogative power to enter into and withdraw from international treaties (such as the one in question, the Lisbon Treaty)? On this point the High Court said that the whole reason why this was a prerogative power was that entering into and withdrawing from international treaties did not usually affect domestic law. However, in this case, withdrawing from the treaty with the EU would certainly have an effect on domestic law and the rights of individuals within the country. The Secretary of State could not therefore use his prerogative powers to withdraw from these particular treaties.

Furthermore, the High Court held that there was nothing in the legislation enacting the European treaties (the European Communities Act 1972) that would indicate that Parliament had intended at the time for withdrawal to be made possible simply by exercise of the prerogative. In other words, the High Court held that Parliament had intended that only Parliament could withdraw from the treaty, in the usual way, and following a vote in the House of Commons.


The case has been fast tracked to the Supreme Court, and it appears that it will be heard in early December.

It is important to note that both parties in this case agreed that the Courts should quite properly have jurisdiction over this matter.

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