On 23 June 2016 the UK voted in a referendum to leave the European Union. While non-binding, the new government has said that the Brexit vote will be given effect.

The response in the UK to the referendum result was an outpouring of emotion and a cessation of effective government and opposition. However, within hours of the result, David Cameron resigned and a new government was quickly formed under his replacement as Prime Minster, Theresa May. As was always going to be the case however, the real result of the referendum has been to stir the debate further, not to put an end to it. Mrs May has said that “Brexit means Brexit”, but that is like saying ‘breakfast means breakfast’, and is no definition at all. The debate about the precise terms on which we leave the EU and our relationships with the rest of the world will rage for years, possibly decades. All we know for certain at the moment is that the real process of withdrawal from the European Union, i.e. the triggering of Article 50 of the Treaty of the European Union, will happen in March next year.

Constitutional position

Article 50 provides that it is for the United Kingdom to decide to withdraw from the European Union according to its own “constitutional requirements”. The United Kingdom has no codified constitution however, and there are competing theories as to what our constitutional requirements actually are. The Government is of the view that it can trigger Article 50 utilising its power under the Royal Prerogative, which allows the Government, on the Sovereign’s behalf, to conduct foreign affairs and enter into international treaties.

The other view is that Parliament must decide to trigger Article 50, either by means of an Act or otherwise.

This is of course a political rather than legal argument; those who are in the Royal Prerogative camp will tend to be Brexiteers. Those who are in the Parliament camp are likely to be Remainers. As is frequently the case in political arguments, however, the courts have been called upon to adjudicate. But the real reason for the fight is not an argument about the finer points of our constitution. It is whether Parliament should be given the right to subvert the will of the people in determining the issue of sovereignty. It is classic Oliver Cromwell stuff. The Parliamentarians believe that if they win and Parliament must legislate, then that will effectively put an end to Brexit because the majority of MPs are in favour of remaining in the EU. The Brexiteers’ concerns are the same. They want the government to trigger Article 50 under the Royal Prerogative because that way Parliament will not have a say.

The question for the court is whether any obligations arising from international law treaties take effect at domestic level until Parliament chooses to incorporate all or part of the international law into the domestic sphere, or whether the Royal Prerogative applies.

The Royal Prerogative has always contained powers relating to foreign affairs. Historically this has involved the making of treaties at international level. While the Constitutional Reform and Governance Act 2010 requires that treaties are laid before the Houses of Parliament for a period of 21 days before they are ratified, the ability of the Government to ratify treaties remains a prerogative power, as does the power to amend or withdraw from treaties.


The argument on the other side is that there is a wider constitutional principle which is that it is not open to the Government to take such a fundamental and irreversible constitutional step by exercise of the prerogative powers. I doubt whether the court will agree with this view. The more likely outcome is that the court will decide that the Government can use the Royal Prerogative power of foreign affairs to trigger the Article 50 process. This is because our constitutional arrangements leave it to the Government to conduct foreign affairs. In this way, the Government can, and has always been able to, activate Article 50 whenever it likes.

For further information please contact David Golten.