Sir Graham Brady - chairman of the 1922 Committee of backbench Tories - is expected to announce on Monday morning there will a vote of no confidence in Boris Johnson.
If the format follows previous occasions then Sir Graham will make a short statement to the cameras and a secret ballot of Tory MPs would then follow within days, ITV News' UK Editor Paul Brand reports.
Tory rebels believe the magic number of 54 letters - the number needed to trigger a vote of no confidence - has already been reached and will be announced on Monday morning.
Only Sir Graham knows how many letters have been received, but he does not reveal the number until publicly declaring the threshold has been reached.
Almost every day last week Tory MPs declared they had submitted letters of no confidence in Mr Johnson.
More than 30 Conservative MPs have publicly urged the PM to resign amid the fallout from revelations about Downing Street parties held during the Covid lockdown, however they have not all confirmed whether they have submitted letters.
Jesse Norman became the latest Tory MP to announce that he had submitted a letter to Sir Graham.
In a letter to the prime minister posted on social media, Mr Norman, the MP for Hereford and South Herefordshire, said Mr Johnson had presided over “a culture of casual law-breaking” in No 10 and that his claim to be vindicated by the Sue Gray report was “grotesque”.
The former minister said Mr Johnson’s current policy priorities were “deeply questionable” and that there were no circumstances in which he could serve in a government led by him.
As well as facing trouble on his backbenches, Mr Johnson also faced public backlash during the Platinum Jubilee bank holiday weekend, including being booed on Friday by some sections of a crowd during his arrival at a thanksgiving service for the Queen at St Paul’s Cathedral.
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As pressure continues to mount on the PM, the biggest challenge facing his party is a lack of a clear candidate to replace Mr Johnson.
Jeremy Hunt, Tom Tugendhat, Penny Mordaunt, Liz Truss and Rishi Sunak are among the names touted to be the next party leader.
But with party MPs seemingly unconvinced that any of them could be an electoral success, some MPs have stopped short of pulling the trigger on the prime minister.
Tory fears about their leader’s standing among the public are also likely to have been fuelled by polling carried out ahead of the Wakefield by-election by JL Partners.
The survey found the Conservatives could lose the key seat by as much as 20 points to Sir Keir Starmer's party this month.
There are also concerns that the upcoming Tiverton and Honiton by-election due to be held on the same day, Mr Johnson faces the prospect of losing seats to Labour in the north of England and the Liberal Democrats in the South West.
The by-elections will be the first electoral test for the governing party since senior civil servant Sue Gray’s investigation into coronavirus rule-breaching events in No 10 and Whitehall was published last month.
What is the process for backbench Tories to remove their leader?
Tory MPs are able to force a vote of no confidence in their leader if they won't resign.
To do so requires 15% of the parliamentary party to submit letters of no confidence to the 1922 Committee, which is effectively a HR department for backbenchers.
It would take 54 letters of no confidence to trigger a secret ballot, with a simple majority required for either side to win.
If more than 50% of Tory MPs vote to remove him, he will lose his role of party leader and be barred from competing in the forthcoming leadership election.
If the leader wins over half the votes, then they remain party leader and are given a year's immunity from any further confidence votes.
If a party leader loses a confidence vote then they will be banned from standing in the forthcoming contest and MPs from across the party can be nominated as potential replacements.
The 1922 Committee will determine how many nominations an MP will require to appear on the ballot.
If more than two qualify then MPs will vote on their preference, leaving two final candidates who must then appeal to party members for votes before being elected leader.