The showdown was dramatically delayed, almost certainly until the new year, after the prime minister admitted a Tory revolt meant she was heading for a crushing defeat “by a significant margin”.
But condemnation of Ms May for pulling back rose when Downing Street failed to set a new timetable for the vote, arguing it depended on when she could “get the assurances” from the EU to pass the deal.
Government sources admitted a quick breakthrough was unlikely, suggesting the vote would be shelved until the new year and refusing to say it would even be held next month.
In extraordinary scenes, Labour MP Lloyd Russell-Moyle was ejected from the House of Commons for seizing the ceremonial mace in protest at the formal deferral of the vote by the government whips.
Mr Russell-Moyle swung the antique symbol of parliamentary authority from its holder as Tory MPs screamed “expel him”. He was promptly asked to leave the chamber by John Bercow, the speaker.
His intervention came moments after Labour leader Jeremy Corbyn secured an emergency debate on the delay on Tuesday.
The impasse remains the Irish border, where a gulf remains between MPs’ demands for the UK to be able to escape the backstop and the EU’s refusal to renegotiate the withdrawal agreement.
The pound plunged to a 20-month low within minutes of the announcement of the delay, as the markets digested the deepening Brexit crisis.
It came just hours after the European Court of Justice confirmed the UK has the right to cancel Brexit by revoking Article 50 unilaterally, thus remaining in the EU on its current membership terms.
Unless a “meaningful vote” is staged, MPs have no formal mechanism to stop the UK crashing out of the EU with no agreement next March – something the prime minister admitted, for the first time, would cause “significant economic damage”.
The extraordinary uncertainty was condemned by MPs on all sides. Mr Corbyn said: “If the prime minister cannot be clear that she can and will renegotiate a deal then she must make way.”
Justine Greening, the former Conservative cabinet minister, said: “Parliament has gone round in circles on Brexit. Now today, even that’s stopped. Britain must find a direction. Kicking the can down the road again solves nothing.”
And Sammy Wilson, Brexit spokesman for the Democratic Unionist Party – the Tories’ partners in power – turned on Ms May, saying: “Doesn’t she believe that, every time she returns to the House with her tail between her legs, she humiliates the British people?”
A furious Mark Francois, deputy chairman of the hard Brexit-supporting European Research Group of Tory MPs, said the government had “run away and hidden in the toilets”, adding: “What the government have done today is shameful.”
Downing Street also sparked fury by refusing to let MPs decide whether the vote, scheduled for Tuesday evening, should be pulled, despite being all but ordered to do so by the Commons Speaker.
Instead, a government whip will prevent debate continuing on the withdrawal deal on Monday and Tuesday by failing to say “now” at a crucial moment, without a vote taking place.
Mr Corbyn came under fierce pressure from Labour MPs and peers to call an immediate vote of no confidence in the prime minister. More than 50 signed a letter to the party leader.
But a party spokesperson said it would only make the move when it had a realistic chance of success, by persuading DUP MPs or, perhaps, rebel Tories to back it.
That might come “when she brings the same deal back to the House of Commons without significant changes”, the spokesperson suggested.
Continued stalemate in Brussels will increase the danger of a different vote of no confidence – by Tory MPs, if the necessary 48 signatures are collected.
Donald Tusk, the European Council president, offered Ms May a glimmer of hope by agreeing Brexit could be discussed at a planned EU summit, starting on Thursday.
However, he made clear: “We will not renegotiate the deal, including the backstop, but we are ready to discuss how to facilitate UK ratification.” The last words hinted at warmer words, but no big shift.
In the Commons, Ms May insisted “nothing is off the table” in Brussels – but repeatedly said she was seeking “assurances”, rather than the renegotiation MPs are demanding.
Cabinet will be cancelled on Tuesday, when Ms May holds talks with Mr Tusk, Jean-Claude Juncker, the European Commission president, Angela Merkel, the German chancellor, and Mark Rutte, the Dutch prime minister.
However, her spokesman refused to say she would demand a “legally binding” exit mechanism from the backstop, or for the UK to be able to end it “unilaterally” – something the EU has repeatedly ruled out.
If the UK and EU had failed to reach a withdrawal agreement, the prime minister would have been required to make a statement to the Commons by 21 January on what course she would follow.
However, given the agreement was reached, there is no requirement for any motion or statement before Brexit day on 29 March.
Asked to give a “cast-iron guarantee” there would be a “meaningful vote” at some stage, Ms May’s spokesman replied: “Yes. We are leaving the European Union on 29 March and we are committed to doing so with a deal.”
Earlier, cabinet ministers held an emergency conference call mid-morning, at which there was “ strong support” for pulling the vote, a No 10 aide said – with no dissenters.
However, there was added pressure on the prime minister on Monday evening when it emerged that the MP Crispin Blunt has sent a letter of no confidence in Ms May to the chairman of the 1922 Committee, the 26th MP in the party to do so, according to The Times.
A challenge to the PM is triggered if 48 Conservative MPs write letters demanding a confidence vote to Sir Graham Brady, chairman of the committee.
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