Twenty newer Tory MPs, who won their seats in 2019, held a secret ballot on Tuesday to find out how many had submitted letters of no confidence in the prime minister, and it emerged that over half had already done so.
Some present said they believed others were likely to follow suit on Wednesday - in a move that could increase the number of letters to the 54 required to trigger a confidence vote in Boris Johnson's leadership.
The group decided not to make a public statement - in order to protect other colleagues - but some told ITV news they were furious and felt that Mr Johnson had lied to them.
Their plotting lead to a backlash from Cabinet ministers and others, who attacked the group, claiming Mr Johnson was the reason they won their seats.
One MP texted to say: "These 109s are a load of arrogant twats who believe their own hype.
"Boris won those seats for them. It wasn’t their good looks and charm."
A cabinet minister was quoted as saying they were "nobodies".
Tory whips were told to head out across Parliament, including to the tearooms, to try to persuade potential rebels to think again. They called for "stability", according to one source.
But some of the MPs told ITV news they were just too angry.
One said the turning point was realising that when Mr Johnson reacted angrily to the tape of Allegra Stratton and other advisers joking about an alleged party, "he was lying to us".
It takes 54 letters to Sir Graham Brady to trigger a confidence vote. If Johnson wins he cannot be challenged for another year.
But if he loses, he will be forced from power.
Names being discussed as possible replacements are the Chancellor Rishi Sunak, foreign secretary, Liz Truss and others such as Penny Mordaunt and even Sir Graham Brady- although none have revealed publicly that they want the job.