Keir Starmer is facing growing calls from furious Labour MPs to give Morgan McSweeney the sack.
Labour MPs rounded on Mr McSweeney for advising Sir Keir to appoint disgraced Peter Mandelson as US ambassador - and called for the official to be fired in order to save the imperilled Government.
It comes as reports yesterday revealed that a think-tank once led by Mr McSweeney had paid thousands of pounds for a firm to investigate journalists looking into its bankrolling of Sir Keir's campaign for Labour leader.
Downing Street on Thursday said the PM retained confidence in Mr McSweeney - but Labour backbenchers warned he would continue to be an albatross around the PM's neck if he were not fired, with eight MPs publicly calling for his head.
Liverpool Riverside MP Kim Johnson yesterday joined in condemning the Downing Street chief of staff - who championed Mr Mandelson's appointment while knowing of his relationship with paedophile Jeffrey Epstein - saying: 'McSweeney's operation is rotten to the core.'
Labour MP for Alloa and Grangemouth Brian Leishman added it was 'time he was removed from power'.
Karl Turner, the Labour MP for Kingston upon Hull East, said: 'If McSweeney continues in No 10 Downing Street, I think the PM is up against it in a way that he doesn't need to be.'
Stroud MP Simon Opher said the PM is being 'badly advised and really let down' and needs to 'change his advisers'.
The MPs' comments come as polling released this week revealed that just five per cent of voters had not heard about Mandelson's involvement with Epstein.
Mandelson was given the post of US ambassador in December 2024, despite the Prime Minister admitting this week that he had known the former peer had remained friends with Epstein after he was convicted of child sex offences.
While the Prime Minister has faced calls for him to tender his own resignation, a growing chorus of Labour MPs are calling for his chief adviser to be sacrificed in his place.
One Labour MP told the Daily Mail Mr McSweeney had become a 'distraction on steroids', and that all they are hearing from voters is: 'When's the leader going to get rid of his adviser?'
While Labour started the new year trying to shed unpopular policies - what's known as 'scraping the barnacles off the boat' - the MP quipped: 'We've got too many barnacles, not enough boats.'
A former minister told the paper MrMcSweeneyhad presided over a 'factional coup' to fill the Government with Starmer loyalists in its September reshuffle and that their 'goodwill bank has dried up'.
But Left-winger Rachael Maskell, who initially joined calls for Mr McSweeney to be fired, appeared to call for unity after meeting with the Prime Minister at Chequers, his country residence, on Thursday evening.
She said: 'If he sacked Morgan McSweeney, we would be in a much stronger place, but he has decided to stand by him.'
Ms Maskell was branded a 'complete hypocrite' by another Labour MP who said she was 'more than happy to enjoy Keir's hospitality' despite calling for his resignation just hours earlier, in comments shared with The Sun.
Mr McSweeney was coming under more pressure yesterday as reports emerged of his involvement in a sting operation against journalists.
Influential think-tank Labour Together, which Mr McSweeny once ran, paid a PR firm at least £30,000 to investigate journalists from the Sunday Times, the Guardian and other media outlets to sniff out their sources, documents shared with the Democracy for Sale Substack revealed.
Labour Together would not respond to a request for comment.