Supreme Court set to rule who has power to trigger Brexit

Prime Minister Theresa May holds a regional Cabinet meeting. Picture: Stefan Rousseau/PA Wire

The decision of 11 judges will determine whether Prime Minister Theresa May can invoke Article 50 of the Lisbon Treaty herself, or if she needs the permission of Parliament to do so.

The judgment follows a ruling by the High Court in November stating that Parliament has the final say on officially deciding that the UK wishes to leave the European Union.

The Government appealed that ruling to the Supreme Court as Mrs May has always claimed it is within her powers to trigger Article 50, which the Prime Minister has said she intends to do by the end of March.

The highest court in the land is to decide whether to reject or allow the Government appeal against the High Court judgment which blocked the royal prerogative being used to launch Britain’s exit from the EU without Parliament having a say.

A case of significant constitutional importance saw three High Court judges unanimously decide that Mrs May did not have authority to use Crown “prerogative powers” to invoke Article 50 to start the two-year process of negotiating the UK’s departure from the EU.

Businesswoman Gina Miller, the lead claimant in the High Court case, has insisted the legal action was not aimed at stopping Brexit, but ensuring the supremacy of Parliament in the process.

Despite the narrow Leave win in June’s referendum by a margin of 51.9% to 48.1%, constitutional experts point out that the poll was a consultative plebiscite and not a binding instruction to parliament.

If it is ruled Parliament must decide on the matter, MPs could be able to table amendments to the measure, such as obliging the UK to remain within the single market after withdrawal from the EU.