Labour MP Graham Stringer has urged the Prime Minister to set out a timeline for his departure, arguing he will "not survive" until the end of this parliament.
Speaking to GB News, the veteran backbencher said: "I don't think the Prime Minister can survive for the rest of this parliament, which is the real issue here."
Mr Stringer stopped short of demanding an immediate resignation, warning this would create "a huge hole in the middle of Government".
Instead, he called for a planned exit that would allow Labour to properly debate its future direction and select a new leader.
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"He needs to make plans for him to go in as dignified a way as possible, dignified for the sake of the country, for the sake of the Labour Party," Mr Stringer added.
The MP expressed profound disappointment with the Government's performance, pointing to 18 policy reversals as damning evidence of dysfunction.
He argued: "There have been 18 U-turns. Nothing wrong with a U-turn if you make a mistake and you realise the mistake.
"But 18 mistakes that have needed rectifying is the hallmark of a Government that doesn't know what it's doing and a leadership that is not leading."
Graham Stringer has called on Keir Starmer to resign over the Peter Mandelson scandal
|GB NEWS / PA
Mr Stringer drew unflattering parallels with the previous administration, noting that the disorder which plagued the Conservatives has continued under Labour.
He revealed that senior Tory cabinet ministers had confided their disappointment to him just months after the election, having hoped Labour would at least deliver stable governance after their own party's turmoil.
"So I am enormously disappointed for the country and for the Labour Party," Mr Stringer concluded.
He argued that Britain faces an exceptionally challenging period requiring robust leadership capable of making unpopular choices.
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"This country is in a very difficult situation, tough decisions have to be taken about defence, about the economy, about benefits, about energy policy," he said.
The MP warned that whoever leads must be prepared to weather intense opposition, as policy changes will inevitably create losers.
He highlighted the precarious international landscape, noting that at least two or three major nations are "extraordinarily hostile" towards the UK.
"And those sort of decisions have to be taken by somebody who is strong enough to withstand what is likely to be a ferocious debate," Mr Stringer explained.
Mr Stringer told GB News that he is 'extraordinarily disappointed' in Keir Starmer
|GB NEWS
Turning to potential successors, Mr Stringer expressed scepticism about whether any current cabinet member could perform better in the role.
He specifically mentioned Ed Miliband, whose name has been floated as a possible replacement, but suggested he and most other cabinet colleagues should rule themselves out.
"It's not been clear to me that there has been proper collective debate and discussion when things have gone wrong in the cabinet, so I'm not persuaded that the names being put forward at the moment would do a better job," he said.
However, Mr Stringer remained optimistic that a suitable candidate exists within the parliamentary party's ranks.
"There are 400 Labour MPs, and I'm sure we can find somebody who has the ability, determination and the intellect to do it," he added.