Theresa May’s premiership was under fresh pressure after Tory MPs spent nearly an hour war-gaming how to oust her at a private meeting.
Around 50 MPs discussed ways and means of getting rid of the Prime Minister at a gathering of the European Research Group (ERG), the Press Association understands.
A number of MPs told how they had already submitted letters of no confidence to Sir Graham Brady, chairman of the 1922 Committee, and others discussed plans to follow suit.
If 48 letters are handed over a vote of no confidence would be triggered.
At a dinner with the PM’s senior aides, meanwhile, MPs raised “leadership issues”.
Backbenchers told the Prime Minister’s chief of staff, Gavin Barwell, his boss must “chuck Chequers” over a dinner at No 10.
The flurry of activity came after former foreign secretary Boris Johnson launched a fresh attack on the PM’s Brexit plan, claiming it would be “substantially worse than the status quo” for British businesses.
Speaking after the No 10 dinner, Tory MP Andrew Bridgen did not deny suggestions the PM would face a coup.
He told ITV News: “I’ve been told that she will get a full appraisal of comments that were made over the dinner.”
Asked if there would be a coup, he replied: “I think we will just have to wait and see.
“I hope that the Prime Minister will take on board what she’s heard and chuck Chequers.”
Conservative Brexiteer John Baron told ITV: “We were discussing leadership issues.”
Downing Street on Tuesday reiterated that Chequers was “the only serious, credible and negotiable plan which is on the table which both delivers on the will of the British people and which prevents the imposition of a hard border in Northern Ireland”.
Mr Johnson spoke at an Economists for Free Trade (EFT) event on Tuesday attended by a battalion of Tory Brexit big-hitters including Jacob-Rees Mogg, former Brexit secretary David Davis and his ex-deputy Steve Baker, former party leader Iain Duncan Smith and ex-Defra Secretary Owen Paterson.
The ex-minister declined to answer questions from journalists but used a Q&A session at the end of the report launch to make a statement himself.
He said leaving the EU while continuing to accept the single market legislation would expose businesses to rules that may go against their interests.
“That seems to me to be a particular economic risk in Chequers and makes it substantially worse than the status quo,” he said.
The ERG will be unveiling its own alternative plan for tackling the Irish border issue on Wednesday.
The group has faced criticism from opponents who say it has attacked the Government’s plans without coming up with one of its own on one of the main sticking points in discussions between Brussels and the Government.