“It’s like rats in a sack on the WhatsApp group today,” says one glum Tory Brexit-backing MP. “Everyone is turning on each other.”

Another described the mood as “extremely bitter and very depressed” among many more mainstream Eurosceptic Conservative MPs who fear they are on the brink of losing the hard Brexit that was almost in their grasp.

Their ire is directed mainly at the 70 pro-Brexit hardliners who refused to back May’s deal on the second attempt. The holdouts won approval from their Conservative members who want nothing less than a no-deal Brexit and will be decisive in picking the next party leader.

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However, they have come under increasing pressure from fellow Eurosceptic MPs with a more realistic view of what is possible. Andrew Percy, a Brexit supporter who voted against extending article 50, released a video saying he was “so frustrated with Brexiteer colleagues going through the lobbies with those who want to overturn the result” while Maria Caulfield, another fervent leaver, urged European Research Group colleagues to change their minds to save Brexit.

That pressure has only ramped up since the Tory MP Sir Oliver Letwin won his bid to let parliament decide on different plans for softer Brexit, revocation or even a second referendum.

“MPs are having to make finely balanced decisions now as the terrain quickly shifts on almost an hourly basis,” said Michael Fabricant, a Tory MP who voted against the deal at the second attempt but is now wavering. “The Oliver Letwin motion has starkly demonstrated to ERG and other Brexit supporters in the House of Commons that a remainer parliament could enact legislation to thwart Brexit. For that reason, I fear that the accursed withdrawal agreement might now well be the least worst option.”

Out of the 69 holdouts, only a dozen of those have now indicated that they would probably change their mind at a third vote. However, there is momentum in that direction, with more possibly persuaded if Theresa May names a date for her departure at the 1922 committee meeting of backbenchers on Wednesday.

Jacob Rees-Mogg, the ERG leader and a backer of Boris Johnson, was one of the first to hint at a shift in position, saying it was now “very, very difficult” to see how the UK would leave the EU without a deal because of May, the cabinet and parliament’s opposition to that option. If the influential backbencher switches, he is likely to bring dozens of others with him. Even Peter Bone, one very hardline Eurosceptic, did not rule out following suit by voting for the deal, saying he would “cross that bridge when we come to it”.

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Johnson has also left himself an escape route to vote for the deal in an article he wrote for the Telegraph, criticising its “Carthaginian terms” but suggesting he could back May’s plan if there were to be a change in the negotiating team for the second phase – code for the departure of the prime minister.

However, the former foreign secretary faces a dilemma. To enhance his chances of becoming leader, he needs to win round Conservative MPs who are already extremely angry with the holdouts. But his main Eurosceptic rival, Dominic Raab, has been extremely tightlipped about whether he would also fold. Backers of the two men want them to jump together, but neither has made the move yet.

The Democratic Unionist party has also left open the possibility that its MPs could swap sides, publicly squashing a declaration by their own Brexit spokesman, Sammy Wilson, that the deal was so toxic the party would prefer a year-long delay to leaving the EU.

Yet even those big beasts of the Eurosceptic movement may not be enough for May’s deal to pass. A hardcore of up to 30 “Brexit ultras” – such as Steve Baker, Andrea Jenkyns and Crispin Blunt – currently remain resolutely opposed, mainly for ideological reasons. This group believe May’s deal does not amount to Brexit at all and would rather risk their goal than pass up the chance of a clean break with the EU.

At a meeting in Westminster of the Bruges Group thinktank, the Tory backbencher and former ERG chair Suella Braverman won a standing ovation from grassroots activists for insisting she could not back May’s deal without significant moves on the Irish backstop.

“I really want to get back into the government’s lobby, but I’m not going to do that unless there are legally binding and material changes to this arrangement,” Braverman said, urging May to embrace a no-deal Brexit.

“She could turn it around, right now. She could unite the country. Because the polls show very clearly that the British people, even businesses, are now ready and prepared for a no-deal scenario, which brings an end to this pernicious uncertainty.”

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Veteran Eurosceptic Christopher Chope was even more scathing about May personally, asking the audience what word would best describe what he said was a turnaround in her position since her Lancaster House speech in 2017. “Betrayal, treachery, deceit, duplicity, dishonesty, incompetence,” he suggested. “But actually my favourite is chicanery. Because chicanery is defined as an abuse of dissension or subterfuge to achieve one’s purpose.”

He is not alone in such trenchant views. But May’s majority is so slim that she needs the DUP and almost all but around 15 Conservative votes, unless she secures the backing of more Labour MPs.

David Davis, the former Brexit secretary, pronounced on Tuesday night that May’s deal was not dead yet and had a “reasonable chance” of passing. That still looks highly optimistic on current numbers.