Health secretary Wes Streeting is believed to be preparing to launch a leadership bid as scores of Labour MPs joined demands that Sir Keir Starmer quits as prime minister.
The fevered speculation came as a series of junior members of the government allied to Mr Streeting resigned their positions with ministers expected to follow.
The moves came after Sir Keir vowed to prove his doubters wrong on Monday as he clung to power despite growing calls from Labour MPs for him to quit.
His make-or-break speech in central London was met with cheers from his audience in the room, but failed to impress furious backbenchers still reeling from last week’s historically poor election results.
More than 60 Labour MPs from all wings of the party called on the prime minister to go immediately or set a timetable for his departure, and there was growing speculation that Mr Streeting was about to launch a coup.
Several supporters of Mr Streeting joined the growing list of MPs calling for the PM to quit, including Chris Curtis, chair of the growth group, and MPs Josh Simons, Jas Athwal, Sally Jamieson and Tom Rutland. Mr Streeting’s parliamentary private secretary Joe Morris also resigned from the government.
Allies of former deputy prime minister Angela Rayner were also preparing for their own leadership bid, with an expectation that Mr Streeting would make an announcement on Tuesday.
One Labour source said: “Things are going to kick off tomorrow.”
But in a defiant message to his critics, Sir Keir said: “I get it, I feel it, and I take responsibility. I know I have my doubters, and I know I need to prove them wrong, and I will.”
Addressing the challenges posed by Nigel Farage’s Reform UK and Zack Polanski’s Green Party, both of which took hundreds of seats from Labour at the local elections, Sir Keir urged his party to get behind him.
“This is nothing less than a battle for the soul of our nation, and I want to be crystal clear about how we will win it, because we cannot win as a weaker version of Reform or the Greens,” he said.
“We can only win as a stronger version of Labour, a mainstream party of power, not protest.”
He turned on Mr Farage’s “false promises” over Brexit and described the Reform UK leader as “a grifter and a chancer”.
He also vowed to take on the far right, and announced he had banned foreign influencers from joining Tommy Robinson’s march at the weekend.
But while he was cheered in the crowded room of the Coin Community Centre in the City of London, his message failed to impress the wider audience outside.
There was concern that he dodged a question as to whether he would try to block the return of Greater Manchester mayor Andy Burnham to parliament, with support growing for him to replace Sir Keir.
But in a minor boost, potential stalking horse candidate Catherine West, who had previously said she would challenge Sir Keir for the party leadership as early as Monday afternoon in an attempt to force the cabinet to put forward a replacement as prime minister, pulled back from initiating an immediate challenge.
Speaking after Sir Keir’s speech, which she described as “too little, too late”, the former Foreign Office minister said she would now canvass support within the party for the prime minister setting out a timetable for his resignation by September.
MPs noted that allies of the health secretary – notably Chris Curtis from the right-wing pro-growth group – had joined left-wing rebels in demanding the PM stands down.
Many of the leading candidates, including Mr Streeting and energy secretary Ed Miliband, remained silent in the wake of the prime minister’s speech, but Ms Rayner reiterated calls first made on Sunday for Mr Burnham, himself a favourite to take over from Sir Keir, to return to Westminster.
Meanwhile, several MPs said they were disappointed by the PM’s speech, which included very little policy detail. There was a vague promise to put the UK back at the heart of Europe, but no details of how this would happen or if it meant undoing Brexit and setting a path to rejoin.
Sir Keir did confirm that British Steel would be nationalised, but did not follow this up with a new economic policy that either promised the growth desired by the right of the party or the nationalisation demanded by the left.
Newcastle North MP Catherine McKinnell said: “It’s become clear that it is time for a new leader to take us to the finishing line of this term and on to the next.”
Her city saw a wipeout for Labour councillors as Reform took control.
Plymouth Moor View MP Fred Thomas, another previous loyalist, wrote in support of a leadership contest.
He said: “I have nothing but respect for Sir Keir Starmer. He transformed our party and led us to an election victory.
“But sadly it is clear now that to deliver on our promise of change and to secure Britain’s future, we must look to a new leader.”
Some Starmer loyalists hit back at Ms West’s attempts to gather signatures to initiate a leadership election.
Banbury MP Sean Woodcock shared his email response to Ms West, in which he asked her to “please stop”.
“I think this is a wholly unserious way of going about this,” he said.
“While I too had disappointing results in my seat and would describe myself far from happy at where we find ourselves, this is not how the government of a major economy and nuclear power should be decided”.