Boris Johnson’s premiership is in increasing peril, with a group of cabinet ministers preparing to tell him to resign.
Chief Whip Chris Heaton-Harris and Welsh Secretary Simon Hart are among those waiting in No 10 to call on him to go.
They will be joined by Transport Secretary Grant Shapps, the BBC has been told.
It comes as mass resignations from MPs in government roles continue.
Earlier at Prime Minister’s Questions, Mr Johnson said he had a “colossal mandate” from the 2019 election and would “keep going”.
But one in five MPs with government roles have quit since Tuesday evening, and more Tory backbenchers are turning against him.
Levelling Up Secretary Michael Gove told him to go earlier, and Business Secretary Kwasi Kwarteng has told the chief whip the PM should resign.
Mr Johnson has just left Parliament, after making a scheduled appearance before senior MPs on the Commons Liaison Committee.
Under repeated questioning by the committee, he ruled out calling a snap general election, saying the earliest date he can see for one is 2024.
Tory party bosses on the executive of the backbench 1922 committee have postponed a decision on whether to change the rules governing a vote of confidence – but elections to replace the committee will take place next week.
Mr Johnson survived such a vote last month, and under the rules as they currently stand he would be immune from another challenge for a year.
The crisis engulfing Mr Johnson’s premiership began on Tuesday, following the dramatic resignations of Chancellor Rishi Sunak and Health Secretary Sajid Javid.
They quit within minutes of each other following a row over Mr Johnson’s decision to appoint Chris Pincher deputy chief whip earlier this year.
Their departures have triggered a wave of further resignations, with Kemi Badenoch, Alex Burghart, Neil O’Brien, Julia Lopez and Alex Burghart among the latest departures.
A senior ally of the prime minister told the BBC: “It’s now a question of how he exits,” adding the situation was “not sustainable”.
At PMQs, Labour leader Sir Keir Starmer said the Conservatives had become a “corrupted party defending the indefensible”.
He took aim at ministers who have resigned in recent days, saying their decision not to quit before now showed they lacked a “shred of integrity”.
And he rounded on those who have stayed in post, mocking them as a “Z list cast of nodding dogs”, keeping the PM in power.
He added they were “only in office because no-one else is prepared to debase themselves any longer”, calling them the “charge of the lightweight brigade”.
Tory backbencher Gary Sambrook accused the PM of blaming other people for his mistakes and was applauded after calling on him to resign.
Fellow backbencher David Davis, who dramatically called on Mr Johnson to step down in January, repeated his plea for him to quit before “it becomes impossible for government to do its job”.
But Mr Johnson defied calls for him to go, adding he would “continue to deliver on the mandate I was given”.
“The job of a prime minister in difficult circumstances, when he’s been handed a colossal mandate, is to keep going – and that’s what I’m going to do.”