May’s move on the eve of the scheduled parliamentary vote opens up an array of possible outcomes ranging from a disorderly Brexit without a deal to a last-minute deal clinched just weeks before Britain’s March 29 exit or another EU referendum.

Announcing the delay on Monday, May was laughed at by some MPs when she said there was broad support for her deal reached with the EU last month, the result of 18 months of tortuous negotiations, and that she had listened carefully to different views over it.

With her position at home in open jeopardy, May said she would go back to the EU and seek reassurances over the so-called Irish backstop, aimed at ensuring there will be no return to a hard border on the island of Ireland as a result of Brexit.

“If we went ahead and held the vote tomorrow the deal would be rejected by a significant margin,” May told parliament, adding that she was confident it was the right deal.

“We will therefore defer the vote scheduled for tomorrow and not proceed to divide the House at this time,” May said.

The UK would meanwhile step up contingency planning for a no-deal Brexit.

The vote postponement marks what many MPs cast as the collapse of May’s two-year attempt to forge a compromise under which the UK would exit the EU while staying largely within its economic orbit.

It was not immediately clear whether the EU’s 27 other members, which have a combined economic might six times that of the UK, would countenance changes that would convince her domestic opponents to support a deal.

The leader of the opposition Labour Party, Jeremy Corbyn, said Britain no longer had “a functioning government” and called on May to “make way” for a Labour government.

Other smaller parties, such as the Scottish nationalists and the Liberal Democrats, said they would support a vote of no confidence in May’s government.

May indicated she was seeking further assurances from the EU on the working of the backstop, and would seek to give the British parliament more power over its application.

May said other EU leaders were open to a discussion about the backstop, though Germany’s foreign minister said he could not see what could be changed in the 585-page deal.

“Please, prime minister, really do start listening and come back with changes to the withdrawal agreement or it will be voted down,” said Nigel Dodds, deputy leader of the Northern Irish party that props up May’s minority government.

The Democratic Unionist Party are upset as the backstop could align Northern Ireland more closely with the EU than the rest of the UK.

May said the deeper question was whether parliament wanted to deliver on the will of the people for Brexit, or open up the divisions in the world’s fifth-largest economy with another referendum.

“If you take a step back, it is clear that this house faces a much more fundamental question: does this house want to deliver Brexit?” May asked.

Her decision to halt the vote came just hours after the EU’s top court, the Court of Justice, said in an emergency judgment that London could revoke its Article 50 formal divorce notice with no penalty.