Keir Starmer is facing huge pressure to line up Andy Burnham as his successor as Labour braces for a battering in local elections.
The mood among MPs and the Cabinet appears to be turning against the PM as he struggles to shake the Mandelson scandal.
Most are expecting a crisis point when the results of English council, and Scottish and Welsh Parliamentary votes are announced in a fortnight.
Reform is poised to make sweeping gains in former Labour heartlands, while the Greens could storm London. But party insiders fear the situation is already sliding into a 'sh**show'.
Sir Keir has been bolstered up to now by the fact that none of his potential successors are ready to run - including Angela Rayner, who is still wrangling with HMRC over unpaid stamp duty.
However, speculation is mounting that despite his vows to fight on, the drubbing at the polls could force Sir Keir into setting a timetable for his departure.
Keir Starmer has been bolstered up to now by the fact that none of his potential successors are ready to run - including Angela Rayner and Andy Burnham (pictured with Sir Keir earlier this month)
Mr Burnham was blocked by Labour's ruling NEC from standing for the Gorton & Denton by-election in February. Sir Keir's allies argued that he would have needed to vacate the Manchester mayor job, raising the risk it would be won by Reform.
But the Parliamentary contest saw the Greens emerge victorious, overturning a massive majority.
Mr Burnham, a former Cabinet minister, has indicated he is still keen to make a comeback to the Commons.
He has been spotted meeting Ms Rayner, sparking rumours of a 'dream ticket' arrangement, and is expected to campaign for the local elections in London.
Sources have been briefing the Guardian that permitting a return by Mr Burnham could be the price for Sir Keir's survival this summer.
'This has changed in the last few months - MPs have coalesced around Burnham in a way they hadn't before. They also don't want to do what the Tories did with Boris and have a disorderly transition to another insider. They are willing to drag this out until Burnham gets back,' one source told the paper.
'It's Andy or bust,' a centrist MP said. 'Nothing else works. Nobody else can win. Anything before he has a path is too soon.'
However, other senior Labour figures are concerned about pinning hopes on Mr Burnham when he is not even in the Commons currently.
'It is a real sh**show,' one source told the Daily Mail.
Another Labour veteran said of Mr Burnham: 'I mean, he’s got nice eyelashes. But this would very much be out of the annoying voice frying pan and into the Northern fire.'
There have been mounting signs of unrest in Cabinet, with ministers offering only lukewarm support in public and privately criticising the decision to sack Foreign Office mandarin Olly Robbins.
Even Sir Keir's staunchest supporters have been dismayed by his performance amid the latest furore over Peter Mandelson's appointement as US ambassador
The Tories are preparing a bid to trigger a privileges committee probe into whether the PM misled Parliament about Mandelson's vetting.
Even Sir Keir's staunchest supporters have been dismayed by his performance amid the latest furore.
Confronted by broadcasters on a visit to Newcastle yesterday, the premier did not answer 'yes' when asked whether the Cabinet was behind him. And he did not answer 'no' when challenged whether he had considered resigning.
'That's just Keir,' one Labour source shrugged gloomily.