Keir Starmer was clinging to power this evening after the Cabinet gave him a late stay of execution.

The Prime Minister was rocked when the Scottish Labour leader Anas Sarwar dramatically called on him to resign for the good of the country in the wake of the Mandelson scandal.

Mr Sarwar, once an ally of Sir Keir, said there had been ‘too many mistakes’ in Downing Street.

‘I have to be honest about failure wherever I see it,’ he said. ‘The distraction has to end, the leadership has to change.’

Mr Sarwar told the PM of his move in advance, triggering panic in No 10 and sparking a major rescue operation.

One Labour source said ministers were told to voice their support for the PM by the end of the day or face the sack.

Sir Keir was already reeling from the departure of his chief of staff Morgan McSweeney on Sunday, who was followed out of the door by his communications director Tim Allan this morning.

And Cabinet Secretary Sir Chris Wormald was this evening on the brink of joining the Downing Street exodus – just a year after Sir Keir appointed him.

Cabinet ministers had refused to publicly back the embattled Prime Minister for more than 24 hours after Mr McSweeney’s dramatic departure. Private discussions were held about the possibility of replacing him with an interim leader such as Defence Secretary John Healey.

But, with leadership rivals not ready to make their move and financial markets wobbling over the prospect of a chaotic contest, they finally bowed to No 10’s demands to issue public statements of support.

In a belated flurry of posts on social media, which began as Mr Sarwar got to his feet, every member of the Cabinet gave the Prime Minister their broad support.

And in a defiant address to Labour MPs later, Sir Keir vowed to battle on, saying: ‘Every fight I’ve ever been in, I have won.’

On another dramatic day in Westminster:

• Allies of Health Secretary Wes Streeting claimed No 10 had falsely accused him of being in league with Mr Sarwar at the very moment he was recording a TV interview backing the PM
• Mr Streeting published details of his email exchanges with Peter Mandelson in a bid to draw a line under claims by leadership rivals that his ambitions will be derailed by their past friendship
• Messages revealed that Mr Streeting moaned privately about Labour’s performance, including complaining the Government has ‘no growth strategy at all’
• Details emerged of a ‘Rayner for Leader’ website apparently launched by supporters of the former deputy PM and accidentally set live, briefly, last month
• A Find Out Now poll of 2,000 voters found the public want Sir Keir to resign by a margin of 50:22.

Sir Keir started the day isolated after agreeing the departure of Mr McSweeney, who is credited for masterminding Labour’s landslide election victory in 2024.

No 10 was initially unable to persuade ministers to take to the airwaves to defend the PM amid public revulsion at his decision to appoint Lord Mandelson as ambassador to the US despite knowing he had remained friends with paedophile financier Jeffrey Epstein following his conviction for child sex offences.

But Mr Sarwar’s intervention forced senior Labour figures to make a snap decision to either back the PM or move against him.

None of Sir Keir’s likely successors, including Angela Rayner and Mr Streeting, are confident of winning an immediate battle – and Labour sources said there was strong opposition within the party to triggering a contest before vital local elections in May.

This evening, Ms Rayner denied any links to the website, with her team dismissing it as a ‘fake’ that had neither been commissioned by her, nor with her knowledge, while one ally described it as a ‘false flag’ operation. Ms Rayner and Mr Streeting’s decision to back down gives Sir Keir some breathing space to try to regain control of the Government which has been hit with a wave of anger over the Mandelson scandal.

However, Labour MPs warned that Sir Keir could still be forced out if the party loses a looming by-election in Manchester this month or suffers a wipeout in May, when Scottish and Welsh parliamentary elections will be held alongside a major round of council elections in England.

Veteran Labour MP Graham Stringer said the PM ‘cannot survive this amount of chaos’, adding: ‘I think we have to wait and see the [election] results… that will give Labour MPs time to sort through what is the right process.’

Labour MP Peter Lamb urged the PM to name his departure date now. Writing in The House magazine, he said: ‘He can wait until May and force the country to endure the chaos of removing a sitting PM… or he can act now.’

Ministers also warned the PM that he would have to make radical changes to survive. Technology Secretary Liz Kendall backed him to stay to ‘steady the ship’, but added: ‘We also need to change course.’

Education Secretary Bridget Phillipson acknowledged that the Government had ‘made mistakes’ but insisted Sir Keir would still be Prime Minister by the summer.

In his address to the Labour Party this evening, the PM insisted he wanted to stay to take on Nigel Farage at the next election.

‘Having fought so hard for the chance to change our country, I’m not prepared to walk away from my mandate and my responsibility, or to plunge us into chaos, as others have done,’ he said.

Sir Keir went on to describe the battle with Reform UK as the ‘fight of our lives, the fight of our times’.

He added: ‘I’ll tell you this, as long as I have breath in my body, I’ll be in that fight, on behalf of the country that I love and I believe in, against those that want to tear it up.’