Theresa May does not have the authority to trigger Article 50 and take the United Kingdom out of the European Union without the prior agreement of parliament, the High Court has ruled.
The decision means MPs will be granted a vote in the Commons on leaving the EU.
Parliament is highly unlikely to block Brexit - but the ruling does give MPs the ability to demand greater detail from the government on what its negotiating strategy with Brussels is and what new relationship with the EU it will seek to forge.
May argued she had the authority to use the royal prerogative to trigger Article 50 without a vote. She has previously said that MPs who wanted to be given a say were trying to “subvert democracy”.
Government lawyers said prerogative powers are a legitimate way to give effect “to the will of the people” who voted by a clear majority to opt for Brexit in the June EU referendum.
However the High Court disagreed and said May unlawfully intended to by-pass parliamentary scrutiny while taking irreversible steps to remove statutory rights granted to UK citizens under the European Communities Act 1972, which made EU law part of UK law.
The government has decided to appeal against the ruling at the Supreme Court. And Downing Street said it had “no intention of letting this decision derail our timetable for triggering Article 50”. May has said she will start the Brexit process by the end of March 2017.
International Trade Secretary Liam Fox said he was “disappointed” at the High Court decision, adding: “the Government is determined to respect the result of the referendum”.
Jeremy Corbyn said Labour would be “pressing the case for a Brexit that works for Britain, putting jobs, living standards and the economy first”.
“This ruling underlines the need for the Government to bring its negotiating terms to parliament without delay. Labour respects the decision of the British people to leave the European Union. But there must be transparency and accountability to parliament on the terms of Brexit,” he said.
But Ukip leader Nigel Farage said “betrayal may be near at hand” over Brexit. “I now fear that every attempt will be made to block or delay the triggering of Article 50. If this is so, they have no idea of the level of public anger they will provoke”.
And Tory MP Jacob Rees-Mogg suggested the judges were pro-EU. “Every court case brought against a European treaty when powers were flowing to the EU the courts upheld and they upheld the royal prerogative,” he said.
“And now when it’s about taking powers away from the EU, suddenly they’re ruling against the royal prerogative, so I think it’s a very surprising judgement. and we’ll need to look at the politics of it very carefully.”
Liberal Democrat leader Tim Farron welcomed today’s ruling. “Given the strict two year timetable of exiting the EU once Article 50 is triggered, it is critical that the government now lay out their negotiating to Parliament, before such a vote is held,” he said.
“So far May’s team have been all over the place when it comes to prioritising what is best for Britain, and it’s time they pull their socks up and start taking this seriously.
“Ultimately, the British people voted for a departure but not for a destination, which is why what really matters is allowing them to vote again on the final deal, giving them the chance to say no to an irresponsible hard Brexit that risks our economy and our jobs.”
Former Labour shadow Europe minister Pat McFadden said the decision was “a complete humiliation for the Government”.
“This is a positive step but it needs to be more than just a symbolic act,” the leading ‘Remain’ campaigner said.
“It was always wrong for the Government to try to stop Parliament having a meaningful say in how the UK leaves the EU.
“There is a mandate to leave the EU but there is no mandate for a hard, destructive Brexit. The terms on which we leave should be subject to rigorous debate and scrutiny - in Parliament and the country.
“A role for Parliament in the triggering of Article 50 is welcome. But Parliament should have a clear role in the substance of the Brexit negotiations, not just the process.”