A new group within Labour, spearheaded by Andy Burnham, has warned Keir Starmer risks “breaking” his own party.

Mainstream, which launched earlier this week with the backing of the Greater Manchester Mayor, has raised concerns about the political judgement of the Prime Minister.

It was set up amid concern the left of the party was being sidelined by Downing Street following the resignation of Angela Rayner.

The following reshuffle promoted prominent figures on Labour’s Right, such as Shabana Mahmood and Pat McFadden.

Now, Mainstream’s national coordinator Luke Hurst has told The Telegraph: “Peter Mandelson’s inevitable sacking is what happens when you put your party faction’s interest before your party and before the country.

“If Starmer keeps running a narrow and brittle political project, it will break him and could break the Labour Party. We need a Government and party of all the talents and all the views.”

The group’s inception has prompted speculation that the Greater Manchester Mayor, who regularly polls as one of the most popular figures in Labour, could make a return to frontline politics.

Allies close to Mr Burnham, who served as the MP for Leigh from 2001 to 2017, had been exploring ways to get the former Health Secretary a parliamentary seat at the next general election, reports Guido Fawkes.

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It has also been suggested he may throw his hat in the ring for any leadership challenge that may arise, should a vacancy appear.

The Prime Minister sacked Lord Mandelson yesterday after emails emerged in which the peer offered support to Jeffrey Epstein even as he faced jail for sexual offences.

Sir Keir, who had said he had “full confidence” in the former US ambassador before the emails were published, is now facing questions over what he knew and when about his ties to Epstein.

He is also facing anger from Labour backbenchers, some of whom have taken aim at Sir Keir’s chief of staff, Morgan McSweeney.

One Labour backbencher suggested the Mandelson scandal could be “terminal” for Mr McSweeney, but could also prove a serious problem for the Prime Minister.

They said: “I think Morgan McSweeney runs the show, and Keir just enables it and makes very bad decisions. I’m not sure how long this can continue though.”

Downing Street said Sir Keir Starmer still had confidence in his “top team” following questions over his chief of staff.

Asked if Sir Keir still had confidence in Mr McSweeney’s judgment, a No10 spokesman said: ”Of course the Prime Minister has confidence in his top team and they are getting on with the important work of this Government, which has seen us deliver more than five million extra NHS appointments, new NHS league tables to drive up standards for patients, the new defence industrial strategy, which has included things like the £10billion frigate deal with Norway.”

Norwich South MP Clive Lewis has said his fellow Labour MPs were “concerned, slightly downtrodden, a little bit browbeaten” and that there was a “very dangerous atmosphere” in the party.

He told the BBC’s The Week In Westminster programme: “You see a Labour Prime Minister who feels that he’s lost control within the first year.

“This isn’t navel-gazing. This is me thinking about my constituents, this country, and the fact that the person who is eight points ahead of us is Nigel Farage. That terrifies me. It terrifies my constituents, and it terrifies a lot of people in this country.

“We don’t have the luxury of carrying on this way with someone who I think increasingly, I’m sorry to say, just doesn’t seem up to the job.”