A Cabinet minister warned Labour MPs not to “squander” being in Government by infighting to oust Sir Keir Starmer.
Environment Secretary Emma Reynolds issued the plea as the Prime Minister was fighting for his political life after being engulfed by the Lord Mandelson scandal.
He faces another difficult week with his former No10 chief-of-staff Morgan McSweeney and ex-Foreign Office boss Sir Philip Barton due to give evidence to the Commons Foreign Affairs Committee on the vetting storm over Lord Mandelson’s appointment as British ambassador to the US.
Labour is also facing a hammering in the May local elections, including in London where it could lose control of Sir Keir’s Camden council, and is set to lose heavily in Scotland and Wales, according to polls.
Allies of former Labour Deputy Leader Angela Rayner were said to be hoping that a tax affair over her home in Hove, which led to her resignation as Deputy Prime Minister, may have been cleared up with HMRC within weeks.
If it is it would put her in a better place for a leadership race after the May 7 local elections.
An early leadership battle is likely to benefit her as Health Secretary Wes Streeting, who may also seek the top job, has had close ties with Lord Mandelson which could damage his prospect while the scandal surrounding the Labour peer continues.
Mayor of Greater Manchester Andy Burnham would be a strong contender if he had managed to get back into Parliament, but this was blocked by Labour chiefs including Sir Keir.
Amid the febrile atmosphere over Sir Keir’s future, Ms Reynolds gave a clear message to Labour MPs: “We won a general election not even two years ago, and the Prime Minister has secured a big majority for Labour.
“Labour doesn't win elections very often.
“Let's not squander this opportunity to change the country for the better.
“We are the most important and powerful progressive force in this country for changing people's lives for the better. Let's not waste that opportunity,” she added on Times Radio.
Asked about talk of a leadership pact between Ms Rayner and Mr Burnham, she responded: “I have no idea whether there’s any truth in that at all.
“But there's a lot of speculation about leadership, and frankly, I'm here to talk about what the Government is doing to help working people across the country.”
But some Labour MPs believe Sir Keir needs to go for Labour to be able to win back the support of millions more voters.
Graham Stringer, Labour MP for Blackley & Middleton South who has previously warned that Sir Keir could face a challenge after the local elections, said: “The Prime Minister is a busted flush.
“I just want him to leave in the way that enables the party to produce the best leader who will get it out of both the government’s mess and our electoral mess.
“I haven’t spoken to any Labour MP who thinks he should fight the next election.”
Polling of Labour members showed the overwhelmingly majority think Sir Keir has handled the Mandelson affair badly.
However, around two-thirds (61%) think he should not resign over the scandal, while 29% said he should, the Survation poll for Labour List showed.
They were split on whether Labour should change its leadership, with 46% in favour and 44% saying Sir Keir should remain in post.
The PM is facing mounting pressure over the revelations about the Lord Mandelson’s vetting process and his handling of it, including his decision to sack Foreign Office chief Sir Olly Robbins.
On Tuesday the Foreign Affairs Committee is due to hear from Mr McSweeney, widely regarded as a protege of Lord Mandelson.
He resigned in February over his part in the peer getting the coveted job.
The committee will also hear from Sir Olly’s predecessor, Sir Philip, and receive written evidence from Foreign Office official Ian Collard, who Sir Olly said briefed him on the vetting findings that deemed Lord Mandelson a borderline case and leaned towards recommending that clearance be denied.
The Prime Minister argued last week any claims he misled Parliament had been put to bed by Sir Olly’s evidence.
But the Tories have called for Sir Keir to face Parliament’s Privileges Committee, the same body that investigated Boris Johnson over the Covid-19 partygate affair, with reports that a vote on whether to refer the Prime Minister for such a probe could be held on Tuesday.
It is up to Commons Speaker Sir Lindsay Hoyle to decide whether to allow a vote.
Dame Emily Thornberry, Labour chair of the Commons Foreign Affairs Committee, accused the Conservatives of launching the move for political purposes ahead of the May elections.
She also warned it could risk “cutting across” the work of her committee.
“Our constituents might ask have we got the balance right between holding the Government to account and seemingly squabbling among ourselves when there is so much else going on that perhaps Parliament ought be be focusing on,” added Dame Emily, MP for Islington South and Finsbury.
