Government whips have been ordered to return Westminster amid mounting speculation that Theresa May faces the prospect of a vote of no confidence.
The Independent understand the move comes after multiple MPs said they had fired off letters calling for a vote to the chairman of the party's 1922 committee of backbench Tories.
Three MPs, including the former culture secretary John Whittingdale, Ben Bradley and Mark Francois, became the latest Conservatives to call for a leadership contest as opposition towards Ms May's Brexit deal continues to mount.
Asked by the BBC whether he had submitted a letter of no confidence to the chair of the 1922 committee - Mr Whittingdale replied: "Yes, I have sent a letter to Graham Brady."
If Sir Graham receives 48 letters from Conservative MPs expressing no confidence in the prime minister's leadership, he is required to inform Ms May that a vote will be held among Tory MPs.
The prime minister would then have to secure 50 per cent of MPs' vote to avoid being toppled.
But Ms May, who was threatened with a vote of no confidence in the Commons by Tory MP Jacob Rees-Mogg, has so far remained defiant and resisted calls to drop her plans or stand down, adding yesterday: "Am I going to see this through? Yes."
Likening herself to the famously stubborn England batsman Geoffrey Boycott, her cricketing hero, she told reporters: “What do you know about Geoffrey Boycott? Geoffrey Boycott stuck to it and he got the runs in the end.”
In his letter to Ms May on Friday, Mr Francois said it was "something I thought I would never have to do".
He added that now the details are available on the Brexit agreement, "we can truly see how awful it is".
"The prime minister has been surrounded throughout this process by a praetorian guard of highly pro-European senior civil servants who, I believe, have never accepted the result of the referendum," he wrote.
It follows the decision of both Dominic Raab and Esther McVey to quit their cabinet roles in protest at Ms May's Brexit agreement reached between UK and EU negotiators in Brussels earlier this week.
There had been speculation Michael Gove, the Environment secretary, had been considering his position after refusing to take the vacant job of Brexit secretary, but a source close to him said Mr Gove "thinks it is important to continue working with cabinet colleagues to ensure the best outcome for the country".
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