Embattled Sir Keir Starmer has warned his ministers and MPs a challenge against his leadership could "plunge us into chaos", after attempting to win them over with what he called a "radical" plan to change the country.
Sir Keir sought to rally his quarrelling MPs behind a package of new laws, which he said would "end the status quo that has failed working people".
He promised reforms to areas including health, housing and immigration, before meeting ministers and MPs in Parliament.
Sir Keir is battling to save his job after four ministers quit and dozens of Labour MPs urged him to resign, with Health Secretary Wes Streeting thought to be plotting a leadership challenge.
Supporters of Streeting told the BBC they expected the health secretary to challenge Sir Keir for the Labour leadership as soon as Thursday.
Streeting would need the support of 81 MPs to trigger a leadership contest under the Labour Party's rules.
Streeting met the prime minister in No 10 Downing Street for less than 20 minutes on Wednesday morning, after days of intense speculation that he is preparing a bid to replace him.
The prime minister's spokesman said Sir Keir had "full confidence" in Streeting but would not comment on the details of their meeting.
On Wednesday evening, Sir Keir held a series of meetings with Labour MPs and ministers in Parliament, telling colleagues: "We cannot let a leadership contest plunge us into chaos - a challenge would 100% do that."
The BBC has been told there were two meetings, one with ministers of state and one with more junior ministers, and they lasted about 15 minutes.
Ministers told Sir Keir the government needed to act more like insurgents and govern differently, and the prime minister accepted he needed to change.
Streeting and Starmer met shortly before the Labour government set out its legislative programme in the King's Speech, which marked the start of a new parliamentary session.
The legislation announced by King Charles III in the House of Lords included plans to abolish NHS England, to introduce digital ID, limit trials by jury and end the leasehold system in England and Wales.
There were also proposals to nationalise British Steel, fast-track green energy infrastructure, forge closer trading ties with the EU, and invest in major improvements to rail services in northern England.
Outlining the bills in the House of Commons, Sir Keir said the King's Speech was an "agenda of radical reform across our major public services".
He said he was leading an "urgent, activist, Labour government" that "tilts power back to workers, renters and the less fortunate, gives voice to the working class, and all those that the status quo has repeatedly ignored and dismissed".
The language echoes Sir Keir's attempted reset speech on Monday, when the prime minister said "incremental change won't cut it" and promised to "face up to the big challenges" the country faced.
But the prime minister failed to convince many of his MPs that his leadership matches the boldness they believe voters expect from a Labour government.
Speaking in the Commons, Labour MP Jonathan Brash said Sir Keir could not offer the "hope" which the public was "desperate for".
"Some people will say this is about personality," Brash said. "It is not, it's about policy and whether we are prepared to meet the moment with the scale of change it demands."
Brash is one of the more than 80 Labour MPs who have urged Sir Keir to resign immediately or announce a timetable for his departure.
Conservative leader Kemi Badenoch responded to the King's Speech on Wednesday, leaving Labour MPs stony-faced with a string of blistering criticisms of their party's record in government and the prime minister's leadership.
Badenoch said Sir Keir was "in office, but not in power", arguing it was clear "he will not be able to deliver what little there is in this King's Speech".
Turning to Streeting, who was sitting alongside other cabinet ministers on the front benches, Badenoch mocked the health secretary about his leadership ambitions, saying he "has been a bit distracted lately".
"There's no point in giving me dirty looks," Badenoch said. "We all know what he's been up to."
On Wednesday evening, cabinet ministers were working the tearoom and attempting to persuade colleagues a leadership election would "paralyse the ability of the government to get things done for months", and "cause chaos".
Streeting's next move is highly anticipated but there are also other senior Labour politicians who are known to have ambitions to become party leader.
Greater Manchester Mayor Andy Burnham has strong support from Labour MPs and polls suggest he is the most popular Labour politician with voters.
But Burnham is not currently an MP and it would be a tall order for him to get back into the House of Commons, a process that involves winning a parliamentary by-election.
He did apply to be Labour's candidate in the Gorton and Denton by-election earlier this year but was blocked by Sir Keir's allies on the party's ruling body.
Multiple MPs - including Afzal Khan and Jeff Smith - have denied preparing to stand down to allow Burnham to attempt to return to Parliament.
Burnham has pulled out of his regular phone-in radio slot on BBC Radio Manchester on Thursday, as speculation mounted over a potential challenge to Sir Keir's leadership.
A spokesperson for Burnham told the BBC: "As you know, Andy doesn't like to miss the Hot Seat.
"But this week, to get the best deal for Greater Manchester, he has to prioritise discussions arising from last week's local elections."
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