The European Union‘s top court has ruled that Britain may unilaterally reverse its decision to leave the bloc.

In a judgment delivered on Monday, the European Court of Justice said the United Kingdom could revoke Article 50 – the exit clause in the EU’s constitution – “in accordance with its own national constitutional requirements”.

“That possibility exists for as long as a withdrawal agreement concluded between the EU and that Member State has not entered into force or, if no such agreement has been concluded, for as long as the two-year period from the date of the notification of the intention to withdraw from the EU, and any possible extension, has not expired,” it added.

“Such a revocation … would have the effect that the United Kingdom remains in the EU under terms that are unchanged as regards its status as a Member State.”

The UK is due to leave the EU on March 29 next year, two years after it triggered Article 50 and kick-started negotiations with European leaders over a withdrawal agreement.

The case was brought to the ECJ by a group of Scottish politicians opposed to Brexit.

Alyn Smith, one of those who initiated proceedings, described the court’s ruling as “better than we could have hoped for”.

“The timing is sublime. As colleagues in the House of Commons consider Mrs May’s disastrous deal we now have a roadmap out of this Brexit shambles,” Smith, who represents the Scottish National Party in the European Parliament, said.

“A bright light has switched on above an ‘EXIT’ sign,” he added.

EU lawyers had argued during proceedings that revoking Article 50 required consent from the other 27 members of the EU, while the UK government said the court’s views on the matter were irrelevant as Britain would not rescind its triggering of the clause.

Parliament to decide on Brexit plan

The ECJ’s decision, which the court said would “clarify the options open to MPs [members of parliament]”, comes a day before British parliamentarians are due to vote on Prime Minister Theresa May‘s proposed Brexit deal.

The plan has been widely criticised across the political spectrum.

Scores of May’s ruling Conservative Party MPs are expected to reject her proposal, while several opposition parties, including the main opposition Labour Party, have also said they will refuse to back it.

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Unexpected majority support would mean May can introduce a formal EU Withdrawal Agreement Bill to parliament for consideration and ratification in early 2019.

Majority opposition, however, would force the government to put forward a new plan within 21 days.

That could provide May with a window of opportunity to go back to Brussels and push for revised terms of departure from the bloc.

But even if she wins concessions from European leaders, which is not guaranteed, MPs will be able to table amendments on a fresh proposal, potentially forcing the government to alter its Brexit strategy once again.

Alternatively, May might push for a second parliamentary vote on the same withdrawal agreement in the hope the electoral arithmetic is changed by fears that a second rejection would risk a potentially catastrophic no-deal Brexit.

Political events triggered by a parliamentary rejection could derail that entire process, however, and take events out of the prime minister’s hands, with a leadership challenge, general election, second referendum, substantially renegotiated deal or no-deal Brexit all possible outcomes.