Anas Sarwar was left looking isolated after other senior figures in the Labour party failed to back his call for Sir Keir Starmer to resign.

The Scottish party leader called for the Prime Minister to quit in order to save his failing election campaign in Scotland.

Far from boosting his hopes of ousting the SNP at Holyrood he appears only to have created more division in the Scottish Labour ranks and between Holyrood and Wesminster.

Several cabinet ministers – including Scotland Secretary Douglas Alexander and culture minister Ian Murray – came out in support of Sir Keir, leaving Mr Sarwar exposed, even within the Scottish Labour group.

Other Cabinet ministers rallied behind the Prime Minister who later declared he would fight on following a meeting with Labour MPs.

Sir Keir said: “I have had my detractors every step along the way, and I’ve got them now. Detractors that don’t want a Labour government at all, and certainly not one to succeed.

“But I’ll tell you this, after having fought so hard for the chance to change our country, I’m not prepared to walk away from my mandate and my responsibility to my country, or to plunge us into chaos, as others have done.”

He also threw his weight behind Mr Sarwar, saying he backed him “100%” in what was seen as an attempt to prevent chasms opening between Westminster and Holyrood.

Deputy Labour leader Lucy Powell said after the meeting that she saw “more standing ovations and more support than I’ve seen at any recent Parliamentary Labour Party [meetings] than I can remember”.

Just where this leaves Mr Sarwar is a big question facing Scottish Labour who must now also fight on for the next three months in the knowledge that the Scottish leader has disowned his own Prime Minister and is at odds with virtually the whole of the Westminster Cabinet.

Speaking at an unscheduled press conference in Glasgow, the Scottish leader described Sir Keir Starmer as a “decent man” who had dedicated his life to public service and his decision to call for his resignation came after a “lot of thinking over the last few days”.

He said: “I have to do what is right for my country. This isn’t easy and it is not without pain as I have a genuine friendship with Sir Keir Starmer, but my first priority and my first loyalty is to Scotland.

“That’s why the distraction needs to end and the leadership in Downing Street has to change.”

He added that “the failures at the heart of Downing Street” should not be allowed to mean failure continues in Scotland.

Commenting on Downing Street’s mistakes, he said: “Have there been good things? Of course there have – many of them. But no one knows them, and no one can hear them because they are being drowned out. That’s why it cannot continue.”

He said that, like Sir Keir, he had also dedicated himself to public service “and I need to decide what I am willing to accept and what I am willing to tolerate.”

The shock intervention by Mr Sarwar came as a further damaging blow to the Prime Minister whose future hangs in the balance over his appointment of Peter Mandelson as US ambassador. Tim Allan, his director of communications, followed chief of staff Morgan McSweeney out of Downing Street.

Uncertainty over the Prime Minister’s tenure in Downing Street extended to speculation that he might call a general election to avoid the personal humiliation of resigning. However, with Labour lagging in the polls an early poll would almost certainly seal his departure.

Pressure will mount if Labour badly loses the Gorton and Denton by-election on 26 February. Mr Sarwar is holding a pre-election rally on the following day.

Mr Sarwar said he was not backing any particular candidate as a successor to Sir Keir, saying his decision was based only on what was good for Scotland.

He said he had told Sir Keir of his decision ahead of making today’s announcement which quickly appeared to have backfired as a number of Cabinet ministers came out in support of the Prime Minister, notably the Chancellor Rachel Reeves and Deputy Prime Minister and Justice Secretary David Lammy.

They were followed by Energy Secretary Ed Miliband, who said: “This is not the time for the government to turn inwards on itself. We must focus on delivering the change we promised the country.”

Scotland Secretary Douglas Alexander put himself at odds with Mr Sarwar by saying the prime minister “has recognised not just that lessons have to be learned but also that we change how we do government. He is right about that and has my support”.

Ian Murray, the culture minister and Mr Alexander’s predecessor, added to cracks in Scottish Labour, saying: “The last thing we need is more chaos when the public want a government on their side tackling the cost of living.

“We inherited a badly failing economy & public services. That takes time to turn around & Keir deserves that time.

“I’m sorry & deeply disappointed that Anas is wrong here.”

Scottish MSPs showed greater willingness to come out in support of Mr Sarwar, led by deputy leader Jackie Baillie and Mr Sarwar’s predecessor Richard Leonard who was edged out of the role when Sir Keir became party leader.

Opposition parties revelled in the dischord in the Labour party. SNP MP Kirsty Blackman said: “Anas Sarwar would sell his own granny. His latest U-turn reeks of desperation, hypocrisy and opportunism – and raises serious questions about his own role in the Peter Mandelson scandal and the appalling personal judgement he continues to show to this day.

“Mr Sarwar can’t get off the hook. He bragged about Mandelson being an ‘old friend’ despite knowing his close links to Jeffrey Epstein, the world’s most notorious convicted paedophile, were a matter of public record. If Starmer must go – why shouldn’t Sarwar?”

Scottish Conservative leader Russell Findlay said: “This scandal-ridden Labour government are in complete meltdown.

“Anas Sarwar is desperately trying to distance himself from Keir Starmer but Scots will not be fooled. They know Sarwar stood shoulder to shoulder with him throughout the General Election campaign and was only installed as Scottish Labour leader thanks to Starmer intervening to remove Richard Leonard.

“Sarwar cannot escape the blame for the chaos that is engulfing Downing Street given he has backed major decisions from the Prime Minister every step of the way, including the appointment of his old friend Peter Mandelson as US ambassador.”

Scottish Green Party co-leader Gillian Mackay said: “It’s a devastating day for Labour when even Anas Sarwar agrees that the Prime Minister cannot be trusted. 

“How can he ask people to support a Labour party that is led by a man who even he thinks is unfit for office?”

Article updated 10 February