The crushing 149-vote defeat immediately raised questions over the Prime Minister’s future amid growing talk of a General Election.
With her Government in full-scale crisis, Mrs May confirmed a vote will be held tomorrow which could stop the UK crashing out of the EU.
But a huge row was brewing over Mrs May’s motion ruling out a no-deal on march 29 - because it leaves the possibility of crashing out at a later date.
It raised the prospect of a “rolling no-deal” that might postpone the cliff-edge until the end of an extension to Article 50.
Labour MPs said they would put down an amendment tomorrow seeking to rule out no-deal at any time. But Mrs May appeared to be determined to keep the threat alive for the sake of her negotiating hand.
Mrs May’s motion read: “That this House declines to approve leaving the European Union without a Withdrawal Agreement and a Framework on the Future Relationship on 29 March 2019; and notes that leaving without a deal remains the default in UK and EU law unless this House and the EU ratify an agreement.”
If passed, special legislation will be rushed out to remove the legal default of a no-deal on March 29. But under Mrs May’s plans, the possibility will exist until MPs unite behind a plan.
Mrs May’s spokesman said that MPs had “voted for uncertainty” and must now answer the questions raised by the PM about how to proceed.
He would not say if she was now planning to support “indicative votes” in the Commons so that MPs can stage an X-Factor style contest to pick a Plan B, saying only that the PM would see how the votes on no-deal and delay went.
The spokesman also declined to say if Mrs May would attempt to take charge of the process to identify a plan B, saying again that she would watch the outcome of this week’s voting.
The PM has opposed calls for indicative votes so far, including from Cabinet ministers like Amber Rudd, in the belief that they would not produce a solution successfully.
Looking exhausted and her voice croaking, Mrs May insisted that her deal was still the best available.
But facing the threat of mass resignations by ministers, she announced there would be a free vote on stopping a no deal.
She also said MPs will be able to vote on Thursday to delay Brexit beyond March 29.
However, she tersely told MPs that the votes this week would not resolve the Brexit dilemmas.
“Voting against leaving without a deal and for an extension does not solve the problems we face,” she said.
I welcome tonight’s vote to wholly reject the Government’s bad #Brexit deal.
The Prime Minister needs to put our city and our country first, and withdraw Article 50.
It’s time to give the British public the final say. https://t.co/f5wROKGFuC— Sadiq Khan (@SadiqKhan)March 12, 2019
But as MPs digested the small print of the Attorney General’s advice, any hopes that the Prime Minister could win her vote started to evaporate.
A “star chamber” of Eurosceptic lawyers announced at around 1pm that they opposed the Brexit plan and shortly afterwards the Democratic Unionist Party, propping up Mrs May’s government, also came out against it.
As the clock ticked towards the 7pm vote, the number of Tory MPs saying they were changing their stance to support Mrs May rose to 24 but this still left Mrs May way short.
A meeting of the hardline European Research Group broke up just half an hour before the vote, with chairman Jacob Rees-Mogg saying dozens of MPs in the room were expected to vote against the deal.
Brexit Secretary Stephen Barclay ended his winding up speech with an appeal to MPs: “It is time to choose. It is time to support this deal.”
But he was howled down by Opposition MPs minutes before the vote when he claimed that under the Vienna Convention the UK could have “the right to terminate” its backstop obligations if the EU side was guilty of bad faith.
Although Mr Cox nodded along to the claim, the Scottish Nationalists accused the minister of making up fresh legal advice as he went along.
Mrs May’s rollercoaster 24-hours was mirrored in the Pound, which rose last night when she sealed her Strasbourg deal with European Commission president Jean-Claude Juncker, then tanked when the Attorney’s letter came out at 11am - falling 1.43 per cent to 1.15 euros.
It recovered slightly after Mrs May publicly backed ruling out a no-deal exit, to stand at one point down on the day.