Keir Starmer is fighting to quell dissent in his ranks today after dozens of MPs defied his threats to back a standards probe into the Mandelson scandal.
The PM must decide whether to punish 14 MPs who voted for a privileges committee inquiry into whether he lied to Parliament.
Up to 50 more look to have broken a three-line whip on opposing the motion last night - something that would normally lead to disciplinary action.
However, Sir Keir's position is so weak that it is unclear whether he will be able to enforce the dire threats made before the vote.
Labour's huge majority means that the probe was comfortably blocked despite the revolt. Kemi Badenoch said it was a 'cover-up' to protect the premier with a local elections drubbing looming next week. Sir Keir himself did not show his face in the chamber yesterday, although he did vote.
The issue is almost certain to come up again at lunchtime when Sir Keir faces a final PMQs before Parliament prorogues ahead of the King's Speech on May 13.
Keir Starmer is fighting to quell dissent in his ranks today after dozens of MPs defied his threats to back a standards probe into the Mandelson scandal
Labour's huge majority means that the probe was comfortably blocked despite the revolt
Kemi Badenoch said it was a 'cover-up' to protect the premier with a local elections drubbing looming next week
Housing Secretary Steve Reed was deployed to broadcast studios this morning to try to shore up Sir Keir's leadership, insisting the Government would not be 'distracted' by infighting.
The PM is already believed to be plotting ways of surviving the expected disastrous local election results next week. There are claims he has asked Angela Rayner to return to the Cabinet in a reshuffle as soon as next week.
After a day of high drama at Westminster, MPs eventually voted against an inquiry by 335 votes to 223. The 112 margin was significantly lower than the Government's working majority of around 165.
Kemi Badenoch said Labour would 'rue the day' they stood in the way of the probe. 'What's he so scared of? He knows that he has misled Parliament so what he is doing is trying to cover up,' she jibed at Sir Keir/.
Downing Street described the move as a 'desperate political stunt', adding the Government would co-operate with existing parliamentary inquiries into the Mandelson affair.
Mr Reed told Sky News: 'You've got a handful of usual suspects that will repeatedly vote against the Government. They're not going to distract us.
'You know, we've got the renters' rights reforms coming in this Friday, which gives renters, people who rent their home, the biggest increase in protections and rights that we've had for a generation.
'That is what voters want us to focus on, not a handful of people that go off and don't play the team game with the rest of us.
Ninety-nine percent of us are united with the Prime Minister so that we can focus on the issues that matter.'
Parliament's Intelligence and Security Committee (ISC) announced last night that it has finished reviewing papers related to Mandelson's appointment as US ambassador.
The official division list showed 14 Labour MPs defied Sir Keir to back the motion. Cat Smith voted both for and against the motion, which is often called an 'active abstention'
There are claims Sir Keir has asked Angela Rayner to return to the Cabinet in a reshuffle as soon as next week
The Commons ordered the publication of the material in February, amid a wave of fury that almost swept Sir Keir out of power.
The documents are set to include a range of embarrassing messages between ministers and the New Labour architect.
ISC chairman Lord Beamish, a Labour peer, said the committee had 'made exceptional efforts to ensure that it is not holding up the publication of documents' and any delay in publication of the documents was 'in no way due to the committee's part in the process'.
However, the Government could still challenge those decisions at a private committee hearing, and it is unlikely that any further documents will be published before Parliament returns for the new session.