PRIME Minister Sir Keir Starmer must order a full probe into the activities of the right-wing Labour Together faction in the wake of the Mandelson scandal, left MPs said today.

The demand came as dismissed top mandarin Sir Olly Robbins told MPs that Sir Keir had brushed aside all concerns about the suitability of Peter Mandelson to be ambassador to Washington in his haste to push the appointment through, despite Mr Mandelson’s close links to disgraced paedophile financier Jeffrey Epstein.

Sir Olly also revealed that Downing Street had pushed for another disgraced peer, former No 10 communications chief Matthew Doyle, to be handed an ambassadorship, igniting a fresh scandal for Sir Keir.

Mr Doyle was instead named to the House of Lords, but is presently suspended from the Labour Party over revelations that he too had close links to a paedophile.

Sir Olly even told the Commons foreign affairs committee that No 10 had ordered him to keep the plan to make Mr Doyle an ambassador secret from then foreign secretary David Lammy.

Mr Doyle denied, in a statement, seeking an ambassador post.

Authority and political support are now oozing away from the Prime Minister, who appears holed below the political waterline.

In an emergency debate on the crisis, Liverpool MP Ian Byrne said “the public will rightly demand accountability and cultural change. 

“This must begin with a thorough review of the political operation which brought the Prime Minister to power and which clearly continues to carry undue influence over this government.

“So I once again call for a full, transparent and independent investigation into the activities and practices of Labour Together,” a demand also made by John McDonnell and others on Monday.

Left MP Jon Trickett pointed out “Mandelson played a key role in a faction which sought to make the Labour Party into something which it never was,” warning that “if we continue down the path we have chosen we are in a downward spiral from which we may not escape.”

And Bradford East’s Imran Hussein told MPs: “At the heart of this is a toxic and dismissive culture at No 10. At some point we cannot get away from it.

“There needs to be a full transparent inquiry into this whole situation.”

Sir Olly, who was fired from the leadership of the Foreign Office last week for not informing the Prime Minister that Mr Mandelson had not secured approval from the UK Vetting Service for his new job, laid blame for the fiasco at Downing Street’s door.

He claimed there was “constant pressure” from Sir Keir’s team to speed up the approval process, and that they did not seem very interested in whether vetting was carried out or not.

Sir Olly also believed that the Prime Minister ought to have abandoned the idea of sending Mr Mandelson to Washington after receipt of the Cabinet Office’s separate due diligence report, which raised red flags about the New Labour grandee’s record.

“What I feel sad about is that the prime minister’s nominee went ahead despite that due diligence,” he said. 

He was unable to confirm a claim made by one MP that Sir Keir’s then-chief of staff, Morgan McSweeney, had told Sir Olly’s predecessor at the Foreign Office to “just f****** approve” the Mandelson appointment.

His remarks about the plan to appoint Mr Doyle, a long-standing New Labour spin doctor, as an ambassador were explosive.

There were “several discussions initiated by No 10 with me about potentially finding a head of mission opportunity for Matthew Doyle who was then the prime minister’s director of communications,” he said.

“I was under strict instruction not to discuss that with the then foreign secretary, which was uncomfortable.

“I found it very hard to think how I would explain to the office what the credentials of Matthew were to be in an important head of mission role when I was in danger of making very senior, very experienced diplomats” redundant.

“And that’s the point at which I thought that I needed to lay down some markers,” Sir Olly said.

Liberal Democrat leader Sir Ed Davey called the revelation “incredibly damning for Keir Starmer.

“Not content with appointing Peter Mandelson as US ambassador despite his links to Epstein, he tried to appoint another man with a known friendship with a sex offender.

“This is not just a lapse in judgment, it’s a pattern of behaviour.”

Energy Secretary Ed Miliband, often cited as a potential successor to the Labour leader despite his repeated disavowals of any interest in returning to the job, said that both he and Mr Lammy had doubted the wisdom of the Mandelson appointment.

“I steered well clear of Peter Mandelson when I became Labour leader in 2010,” he reminded Sky News, adding that he thought the move “could blow up, that it could go wrong.

“I had a conversation with David Lammy about it before the appointment, and I said I was worried about it. I think he was worried about it too.”

Leeds East MP Richard Burgon also called for a “full independent investigation into Labour Together” which he said had been the vehicle Mr Mandelson and Mr McSweeney had used to get Sir Keir into office and which “has dragged our party into the gutter.”