Theresa May needs the approval of Parliament to trigger the Brexit process, Britain's most senior judges have ruled.

The Supreme Court has decided that MPs must be given a vote on triggering Article 50, the formal mechanism for leaving the European Union.

Despite the setback, Downing Street insisted Mrs May's plan to begin negotiations on leaving the EU by the end of March remains on track.

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Revealing the decision, Supreme Court President Lord Neuberger said: "The referendum is of great political significance, but the Act of Parliament which established it did not say what should happen as a result.


"So any change in the law to give effect to the referendum must be made in the only way permitted by the UK constitution, namely by an Act of Parliament.

"To proceed otherwise would be a breach of settled constitutional principles stretching back many centuries."

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The Government is now expected to quickly publish a short bill in an effort to stick to the PM's Brexit timetable.

A Downing Street spokesman said: "The British people voted to leave the EU, and the Government will deliver on their verdict - triggering Article 50, as planned, by the end of March. Today's ruling does nothing to change that."

Sky's Senior Political Correspondent Beth Rigby said the Government had been preparing for just this outcome since the original High Court ruling in November, and added it sets the stage for "parliamentary fireworks".

While it is thought to be unlikely that the Government will lose a vote, the Supreme Court's decision, by an 8-3 majority, has the potential to hold up the Brexit process.

Shadow Brexit Secretary Keir Starmer: Labour will 'push for amendments'

Labour leader Jeremy Corbyn said his party would not "frustrate the process for invoking Article 50", but would try to amend the legislation to stop the UK becoming a "bargain basement tax haven".

The SNP, the third largest party in the Commons, said it will put forward 50 "serious and substantive" amendments.

The Liberal Democrats, meanwhile, will oppose triggering Article 50 unless the PM promises a second referendum on the final exit deal.

Although the judgment is a blow to Mrs May, the justices unanimously ruled there was no need to consult with the devolved administrations in Scotland, Wales and Northern Ireland.

Image: Lord Neuberger, Lady Hale, Lord Mance, Lord Kerr, Lord Clarke, Lord Wilson, Lord Sumption and Lord Hodge were in the majority

This could have been much more significant in terms of derailing her Brexit timetable.

First Minister Nicola Sturgeon said the ruling raises "fundamental issues" for Scotland, and added it was "inconceivable" the party's MPs at Westminster would vote in favour of triggering Article 50 given Scotland voted to remain in the EU.

Attorney General Jeremy Wright said the Government was "disappointed" with the ruling but would comply with it.

Shadow Brexit secretary Sir Keir Starmer told Sky News it would be "against the spirit of the judgment" if the Government tried to introduce a one-clause bill.

Image: Lord Reed, Lord Carnwath and Lord Hughes were in the minority

The court's ruling said it was "entirely a matter for Parliament" what form the legislation should take.

But it added that even a very brief Act would still have "momentous significance".

The case was won by a wide-ranging group of campaigners, led by investment manager Gina Miller, 51, and hairdresser Deir Dos Santos.

Speaking outside the court, Ms Miller said: "This ruling today means that MPs we have elected will rightfully have the opportunity to bring their invaluable experience and expertise to bear in helping the Government select the best course in the forthcoming Brexit negotiations."