Theresa May has suffered a fresh humiliation over Brexit after her eurosceptic MPs helped Labour to inflict a new parliamentary defeat on the government.

Just 43 days from the UK’s planned exit from the EU, the Prime Minister saw her authority yet again undermined by her own party as the Commons voted by 303 to 258 against her deal.

Just 243 Tories backed May, with nearly a quarter of her MPs deciding to pull their support. Five Tories voted against and 67 abstained.

May had hoped to show Brussels she had a “stable” majority for her recent diplomatic push to revise her plans, but Conservative backbenchers registered their protest as they sought to keep open the option of a no-deal exit.

The defeat was a further embarrassment for No.10, after ministers including international trade secretary Liam Fox had warned Brexiteers that they risked derailing May’s latest bid to get a better deal.

After another dramatic day at Westminster, senior Tory ‘Remainer’ MPs also said they now feared the PM was heading for a no-deal Brexit, by accident or by design.

Seconds after the defeat, Jeremy Corbyn declared that May “cannot keep on just running down the clock and hoping that something will turn up that will save her day and save her face”.

May was absent from the chamber, but a No.10 spokesman said Corbyn was “in effect making no-deal more likely”. Downing Street admitted “there was a concern from some Conservative colleagues about taking no deal off the table at this stage”.

Meanwhile, fury with the Brexiteers spilled over when Tory business minister Richard Harrington told The House magazine that they were guilty of “treachery” and defence minister Tobias Ellwood accused them of being “a party within a party”.

May had won a lifeline a fortnight ago, when the Commons finally agreed a plan to allow her to explore ways to amend the Northern Ireland ‘backstop’, a controversial part of her deal that could keep the UK tied indefinitely to EU trade rules.

But members of the backbench European Research Group (ERG) were furious that the PM’s motion for the Valentine’s Day vote included a tacit commitment to avoid no-deal.

ERG chairman Jacob Rees-Mogg had said that his group would not be voting against the government, but had decided to instead abstain, in effect ensuring a major victory by Labour and other opposition parties.

Earlier, Fox had warned: “Our European partners will be watching our debate and listening today to see if they get the impression that if they were to make those concessions, Parliament would definitely deliver on that.”

Former Cabinet minister Sir Oliver Letwin said he had come to the conclusion that “when the chips are down”, May would prefer to “head for the exit door without a deal…that is a terrifying fact”.

His words echoed those of several sources who told HuffPost UK this week that the PM’s fallback plan was to back a no-deal outcome, in order to preserve her party unity and her legacy as the leader who delivered Brexit.

Fellow Tory Anna Soubry also seized Brexit Secretary Steve Barclay’s claim in the Commons that no-deal was indeed the default position of the government if no agreement could be found by March 29, claiming his words “chilled me to the bone”.

And veteran Conservative Ken Clarke warned May that the ERG group was the Tories’ equivalent of ‘Momentum’, “a kind of breakaway party” made up of “ardent right-wingers”.

Hilary Benn, the chair of the Brexit select committee, added that May’s attempt to bounce MPs into a very late vote on the plan carried a real risk of a no-deal exit.

“We are careering towards the cliff, she’s at the wheel, and the Cabinet are sitting in the back seat. And at some point they are going to have to decide to lean over and take the steering wheel off her. Because if that doesn’t happen then a no-deal Brexit might come to pass.”

Soubry pulled her own amendment demanding secret Whitehall assessments of the impact of no-deal, after minister Chris Heaton-Harris agreed she could discuss in private new plans to publish the material within seven days.

Earlier Commons leader Andrea Leadsom tried to make a joke of the Valentine’s Day context for the big vote.

“It’s Valentine’s Day so I thought a little poem might be in order – Labour is red, Tories are blue, our future is bright, with a good deal in sight, for the UK and our friends in the EU.”

Her Labour shadow Valerie Vaz said she did not find it “very funny” that the Tories were failing to sort their own chaos of Brexit.

Labour’s David Lammy said: ”“This is a Valentine’s Day massacre for the government and a damning indictment of the Prime Minister’s Brexit plan.

“As well as enjoying another humiliating defeat, the government has been forced into publishing its no-deal advice. Now we wait to see what these papers contain.”

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