Prime Minister Sir Keir Starmer is to meet Health Secretary Wes Streeting, one of his potential leadership challengers, this morning, as his government faces an attempt by Labour MPs to oust him from the top job.
The meeting comes after four ministers resigned, including prominent MP Jess Phillips who quit as safeguarding minister, and Streeting ally Zubir Ahmed.
More than 80 Labour MPs also urged Sir Keir to stand down, exposing deep divisions over the prime minister's future.
Sir Keir vowed to get on with governing on Tuesday, while his cabinet allies and more than 100 MPs rallied behind the prime minister, warning against a leadership contest.
But the prime minister's authority has been weakened by the Labour revolt, which came after a dire set of election results last week.
The resignations and turmoil in Downing Street come as Sir Keir's government is due to set out its legislative agenda in the King's Speech.
Streeting is due to meet Sir Keir in Number 10 Downing Street ahead of the event, which marks the start of a new parliamentary session.
The BBC has been told Streeting will not be saying anything that might distract from the King's Speech following the meeting.
The prime minister earlier defied calls to depart No 10, telling his cabinet the country "expects us to get on with governing" and pointing out that a formal leadership challenge had not been triggered.
A leadership election can only be triggered if the leader resigns or if Labour MPs launch a challenge when there is no vacancy.
A challenger wishing to oust an incumbent leader must be supported by 20% of Labour MPs, meaning 81 would need to support a challenger to formally start the process.
Streeting has previously been open about his leadership ambitions and has plenty of support from Labour MPs, particularly those on the centre and the right of the party.
The BBC has been told the prime minister's allies are convinced the health secretary will not be able to produce a list of 81 supporters in his meeting on Wednesday.
Some of Streeting's backers had written letters suggesting Sir Keir had lost the support of the country, and ministers seen as sympathetic to the health secretary have resigned.
But Sir Keir has defied the pressure to go and some MPs on the party's right, who would have been assumed to be Streeting supporters, have signed the statement that says now is not the time for a leadership contest.
Even if Streeting does lack sufficient support, other challenges remain.
The prime minister has pulled out of a meeting with the unions which help fund the Labour Party.
Those unions are expected to issue a statement declaring that Sir Keir should not lead the party into the next general election.
The uncertainty over Sir Keir's job security is an awkward backdrop to the King's Speech.
The King's Speech is expected to include more than 35 bills and draft bills, including immigration, NHS and police reforms, along with a route to potentially nationalising British Steel.
But whether Sir Keir remains prime minister long enough to deliver the legislation promised is an open question in Westminster.
A day of political drama on Tuesday started with the cabinet meeting at which Sir Keir pushed aside calls for him to resign.
A government source told the BBC that at the cabinet meeting Sir Keir had informed colleagues he would not discuss the election results or his leadership, and would only speak to cabinet ministers about those topics "individually".
The BBC understands several cabinet ministers tried to talk to Sir Keir about his leadership after the cabinet meeting but he declined to speak to them.
In a speech aimed at steadying his tottering premiership on Monday, Sir Keir said "incremental change won't cut it" as he promised to "face up to the big challenges" the country faced.
But it was not enough to win over Phillips, who resigned as safeguarding minister.
In her letter, Phillips said "real change" in her role "usually came from threats made by me in light of catastrophic mistakes".
"I think you are a good man fundamentally, who cares about the right things however I have seen first-hand how that is not enough," Phillips said.
"The desire not to have an argument means we rarely make an argument, leaving opportunities for progress stalled and delayed."
Signing off her letter, Phillips added: "I want a Labour government to work and I will strive as I always have for its success and popularity, but I'm not seeing the change I think I, and the country expect, and so cannot continue to serve as a minister under the current leadership."
Phillips' departure followed Miatta Fahnbulleh's resignation as minister for devolution, faith and communities.
She told the prime minister "to do the right thing for the country and the party and set a timetable for an orderly transition".
Alex Davies-Jones also resigned as minister for victims and violence against women and girls.
She called for "bold, radical action" and similarly urged Sir Keir to set out a timetable for his departure.
Zubir Ahmed was the fourth minister to quit on Tuesday, telling Sir Keir in his resignation letter that the public had "irretrievably lost confidence in you as prime minister" and "continuation in office is wholly untenable".
Nesil Caliskan, Natalie Fleet, Catherine Atkinson and Preet Kaur Gill have been appointed as government ministers to replace those who resigned, while Gen Kitchen, Deirdre Costigan and Shaun Davies have been appointed as Labour whips.
Deputy Prime Minister David Lammy said Sir Keir had his "full support", as he urged colleagues calling for him to resign to "step back".
"No one seems to have the names to stand up against Keir Starmer, and for those who are suggesting that he should stand down, they should say which candidate would be better," Lammy said.
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