The first Labour MP has appealed for Sir Keir Starmer to step down as leader, calling for Andy Burnham to return to the parliamentary Labour Party and "become the next Prime Minister".
Norwich South MP Clive Lewis demanded the leadership change in an interview on Friday night.
Mr Lewis said Greater Manchester Mayor, Mr Burnham, should return to the parliamentary Labour Party and "step up and become the next Prime Minister".
The credibility of Sir Keir was damaged this week after a briefing war surrounding alleged coup plotters.
In an attempt to strengthen Sir Keir's position, No 10 aides briefed journalists that he would fight any attempt to kick him out and that removing him would hurt the markets.
However, the move backfired.
Cabinet ministers demanded resignations and Health Secretary Wes Streeting was named as one of Sir Keir's apparent rivals.
Mr Streeting called the briefings "toxic" and "juvenile".
Briefings from No 10 said Sir Keir Starmer would fight against coup attempts
| PAThe Government on Friday backtracked on plans to break a manifesto promise by raising income tax.
Mr Lewis was asked by Channel 4 if the situation was tenable.
"No it's not tenable, frankly," he said.
"And we now need to do what the Prime Minister once said, which is put country before party and, frankly, party before personal ambition."
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Clive Lewis has called for Andy Burnham to step up and become Prime Minister
| GB NewsMr Lewis was further asked if his comments meant Sir Keir should be replaced as Prime Minister.
"I just don't see how this can stagger on without any resolution on the horizon," he said.
"I think the Labour Party, the Labour grandees, the men in grey suits, need to now really seriously think, how do we get Andy Burnham back into this parliamentary Labour Party and let him step up and become the next Prime Minister?
"That's my personal view."
Mr Lewis acknowledged "it won't be shared by everyone".
"But I don't see many other options," he said.
Mr Burnham prompted speculation that he could replace Sir Keir after refusing to say he would not challenge the Prime Minister.
The party is performing poorly in opinion polls and senior members have left the Government.
Angela Rayner resigned as Deputy Prime Minister after an investigation into her tax-dodging.
Labour MP Barry Gardiner claimed on Wednesday that it was common knowledge that party members were discussing how to get rid of Sir Keir.