Boris Johnson is battling to stay in office, amid a growing wave of resignations from his government in protest at his leadership.
New chancellor Nadhim Zahawi has urged unity after his predecessor, the health secretary, and several junior ministers walked out.
But the prime minister has been hit by five further resignations, taking the total to 15 in the past day.
It comes as he prepares for PMQs later and a grilling by senior MPs.
Mr Johnson's premiership has been plunged into crisis following the dramatic resignations of Chancellor Rishi Sunak and Health Secretary Sajid Javid.
They quit within minutes of each other on Tuesday following a row over Mr Johnson's decision to appoint Chris Pincher deputy chief whip earlier this year.
Five further resignations have followed on Wednesday, including education ministers Will Quince and Robin Walker, Treasury minister John Glen, and ministerial aides Laura Trott and Felicity Buchan.
Mr Javid, who has now resigned from Mr Johnson's cabinet for the second time, will make a resignation statement to Parliament later.
Mr Johnson has admitted it was a "bad mistake" to appoint Mr Pincher, despite being aware of misconduct allegations against him.
It followed days of changing responses from No 10 over what exactly the PM knew about Mr Pincher's past conduct when he gave him the job.
Mr Quince, who was sent out to defend the PM in media interviews two days ago, said Downing Street had given him "inaccurate" information.
In a resignation letter, he added he had "no choice" to resign - adding that he had repeated No 10's assurances "in good faith".
The row over Mr Pincher's appointment comes after the PM's relations with his backbenchers have been damaged by the Partygate scandal and unhappiness over tax rises.
He survived a no-confidence vote among Tory MPs last month, meaning under current party rules he is immune from another challenge for a year.
Several key cabinet ministers, including foreign secretary and potential leadership challenger Liz Truss, have rallied round the prime minister.
However, rebel Tories want to use an upcoming vote to the backbench 1922 committee to scrap the year-long gap between contests, making it possible he could face another challenge later this summer.