Keir Starmer is facing another brutal week as loyalists desperately try to save his premiership.
The PM is staring down the barrel of a damaging Commons showdown on whether he misled the House over the Mandelson scandal.
Speaker Lindsay Hoyle is expected to grant a debate on referring Sir Keir to the Privileges Committee - forcing Labour MPs to decide if they can line up behind the floundering leader.
The clashes would happen tomorrow, the same day as Sir Keir's former chief of staff Morgan McSweeney and the ex-head of the Foreign Office give potentially explosive evidence about Mandelson's appointment.
Downing Street has been mobilising the PM's few remaining allies, with Labour veterans Alan Johnson and David Blunkett branding the privileges motion a 'nakedly political stunt'.
However, the fevered mood in the party is intensifying as catastrophic local elections loom next week. There are claims that Andy Burnham has proposed a Blair-Brown style pact to Angela Rayner, making her his deputy if he takes over from Sir Keir.
Keir Starmer is staring down the barrel of a damaging Commons showdown on whether he misled the House over the Mandelson scandal
Sir Keir is struggling to shake free of the long-running row over Mandelson's (pictured) appointment as US ambassador
Labour MPs are braced for a moment of maximum political danger for the premier if the results are as bad as many fear.
Sir Keir will try to move on again this morning with a speech on domestic policy in the North West.
Mr McSweeney - who resigned in February - will be grilled by the foreign affairs committee on his role in the appointment of Mandelson.
The MPs will also hear from Sir Philip Barton, who was head of the Foreign Office before Olly Robbins - summarily sacked last week for not telling Sir Keir that security vetting checks red-flagged Mandelson.
Foreign Office official Ian Collard, who Sir Olly said briefed him on the vetting findings, will also be giving written evidence.
The PM said last week any claims he misled Parliament had been put to bed by Sir Olly's evidence.
But the Tories have called for Sir Keir to face Parliament's Privileges Committee, the same body that investigated Boris Johnson over the Covid 'Partygate' affair.
It is up to Commons Speaker Sir Lindsay Hoyle to decide whether to allow a vote, which would be likely to happen tomorrow.
That could also derail plans for tidying up a swathe of legislation before Parliament prorogues - which No10 had been hoping would happen before PMQs can be held on Wednesday.
Yesterday Cabinet minister Darren Jones accused the Conservatives of 'using tactics' ahead of local elections on May 7.
The clashes would happen tomorrow, the same day as Sir Keir's former chief of staff Morgan McSweeney gives potentially explosive evidence about Mandelson's appointment
There are claims that Andy Burnham has proposed a Blair-Brown style pact to Angela Rayner (pictured), making her his deputy if he takes over from Sir Keir
Mr Johnson and Lord Blunkett released a joint statement calling the move a 'nakedly political stunt with no substance' ahead of the polls.
They said a referral to the watchdog would be a waste of public money and that comparisons with Mr Johnson are 'absurd'.
'When Parliament referred that matter to the Privileges Committee, a police investigation had directly disproved his categoric statements that he knew nothing about the breach of lockdown rules including parties in Downing Street, and therefore he had a case to answer for knowingly misleading the House of Commons,' they said.