Key Brexiter says he has written to chair of 1922 Committee, in move that could lead to Tory leadership challenge

The leading Brexiter Jacob Rees-Mogg called for a vote of no confidence in Theresa May on the most perilous day of her premiership, after claiming she had broken her own red lines on Brexit.

The outspoken chair of the European Research Group (ERG) of Tory Brexiters, who rejected the prime minister’s plan moments after it was published on Wednesday night, announced he was submitting a letter to the chair of the backbench 1922 Committee, Sir Graham Brady.

Up to a dozen other Tory backbenchers have confirmed they have submitted letters calling for May to step down over her Brexit proposal, including the former Brexit minister Steve Baker and fellow leavers Nadine Dorries and Andrew Bridgen.

Rees-Mogg’s decision came while May was continuing to face a barrage of questions from MPs about her Brexit deal, and while Downing Street was still reeling from a string of resignations, most damagingly that of the Brexit secretary, Dominic Raab.

Quick guide How would the Tories trigger a leadership contest? Show Hide No-confidence proceedings Forty-eight Conservative MPs would need to back a no-confidence vote in Theresa May to trigger a leadership contest, according to party rules. There are two ways a contest can be triggered, most obviously if the leader of the party resigns. If they do not, 15% of Conservative MPs must write to the chairman of the 1922 Committee of backbench Tories. With the party’s current crop of 317 MPs, 48 would be needed. After David Cameron announced his resignation, five Tory MPs stood for the leadership. Unlike Labour party rules, under which candidates go to a ballot of members as long as they have the support of 15% of the party’s MPs, Conservative candidates are whittled down to a final two before party members have their say. The ballot is based on “one member, one vote”, but in 2016 one of the final two candidates, Andrea Leadsom, withdrew from the race after a damaging interview with the Times about the fact that May did not have children. Her withdrawal meant May was made party leader without having been elected by members.

ERG members had previously suggested they would continue to support the prime minister while opposing her Brexit policy. But in his letter, which was released to the media, Rees-Mogg suggested May had broken her word.

“It is of considerable importance that politicians stick to their commitments or do not make such commitments in the first place. Regrettably, this is not the situation, therefore, in accordance with the relevant rules and procedures of the Conservative party and the 1922 Committee, this is a formal letter of no confidence in the leader of the party, the Rt Hon Theresa May,” he wrote.

If Brady receives 48 such letters, he is obliged to trigger a confidence vote. Downing Street confirmed on Thursday that May would contest such a vote and expected to remain prime minister until the Brexit process is complete.

She would need the backing of 158 Tory MPs to see off the Brexiters’ challenge, and her position would then be safe for 12 months.

Raab, whose resignation posed the most serious threat yet to May’s Brexit strategy, insisted he was not encouraging MPs to unseat May. He told Sky News: “I think we need to support this prime minister in getting Brexit over the line and making a success of Brexit. So I don’t want to be part of that sort of discussion or debate.”

Earlier, Rees-Mogg challenged May directly in the House of Commons, saying the Brexit deal published on Wednesday night would keep Britain in the customs union and threaten the integrity of the UK.

“As what my right honourable friend says and what my right honourable friend does no longer match, should I not write to my right honourable friend the member for Altrincham and Sale West?” Rees-Mogg asked her, referring to Brady.

Senior Brexit-backing MPs including Boris Johnson gathered to discuss their strategy in a Westminster committee room amid chaotic scenes. Passing by the room, the Foreign Office minister Alastair Burt expressed fury at events that were unfurling inside. “We are working our socks off and they are doing everything they can to detonate it,” he said.

MPs trickled out to speak to waiting journalists but few admitted putting their names to a confidence motion. Simon Clarke, the MP for Middlesbrough South, was one of the few to confirm he had done so – a resubmission, having withdrawn it several weeks ago.

Johnson, the former foreign secretary, left the room tight-lipped, refusing to confirm or deny he had written to Brady. He is understood to be concerned that any involvement in a plan to oust May could damage his own future leadership hopes.

Sir Edward Leigh, another Eurosceptic former minister leaving the meeting, said there was considerable difference of opinion in the room. “If this coup d’etat succeeds, what happens then? The best way to defeat this deal is to defeat it in parliament, in my view.”

Baker told the meeting: “We’ve tried everything to change policy but not the prime minister, but it has not worked. It is too late. We need a new leader.”

But one Tory ERG member who had decided not to put in a letter said: “Changing leader does not change parliamentary arithmetic. The ERG has never been a cohesive group with an agenda, it’s a flexible coalition of Brexiters.”

Later, outside the House of Commons, Rees-Mogg was mobbed by reporters and camera crews as he gave a press conference at the same spot where May addressed a crowd after winning the Tory leadership.

He suggested several Brexiters as potential successors to May as prime minister, including Johnson, David Davis, Raab and Esther McVey – who all quit the government over the prime minister’s plans – as well as international development secretary Penny Mordaunt. However, he ruled himself out for a run at the leadership.

Brexiters believe that even if May can survive a no-confidence vote – and her aides believe she would – their show of strength could force her to stand down anyway.