Sir Keir Starmer has insisted he has “never authorised” attacks on his cabinet ministers, calling briefings against them “unacceptable”.

The PM was speaking at Prime Minister’s Questions after some of his allies told numerous media outlets he could face a leadership challenge from another cabinet minister such as Health Secretary Wes Streeting.

There has been speculation about the extent to which Sir Keir was aware of the anonymous briefings, which had been aimed at shoring up his position, or had encouraged them in some way.

Streeting has denied he was lining up a leadership bid, and called on those behind the briefings to be sacked.

Asked at an NHS conference in Manchester if he would fight alongside Sir Keir if there were any plots to oust him as PM, Streeting said: “Yes.”

“The bizarre thing about some juvenile briefing overnight is it’s people in No 10 who’ve said the PM is fighting for his job.

“I don’t think that’s a helpful or constructive thing to say, I also don’t think it’s true,” he added.

Streeting earlier attacked the “toxic culture” in Number 10, a comment seized on by Conservative leader Kemi Badenoch, who said the PM had “lost control of his government… and lost the trust of the British people”.

Badenoch said Morgan McSweeney, the Downing Street chief of staff, was responsible for the culture in No 10 and asked if the prime minister still had confidence in him.

Sir Keir replied: “Morgan McSweeney, my team and I are absolutely focused on delivering for the country.

“Let me be clear, of course, I’ve never authorised attacks on cabinet members, I appointed them to their post because they’re the best people to carry out their jobs.”

Sir Keir told MPs “any attack on any member of my cabinet is completely unacceptable”.

He said Streeting – who missed PMQs to deliver a speech at the NHS conference – was doing a “great job” cutting waiting lists and boosting the number of doctors.

Speaking after PMQs, the prime minister’s press secretary told reporters the briefings against Streeting had come “from outside No 10” and that the prime minister had full confidence in McSweeney.

The spokesperson refused to say whether there was a leak inquiry, but did say leaks would be “dealt with”.

Briefings of this nature are often part of reporting on politics in Westminster, when people speak to journalists “off the record”.

This means they say things that they are not prepared to say on camera, which the BBC reports in order to give the full story.

On Tuesday evening, supporters of the prime minister told journalists he would fight a challenge to his leadership, which they believed could come as soon as after the Budget on 26 November.

They argued that removing the PM could create chaos, destabilise the international markets and damage the relationship he has built with US President Donald Trump.

The names being discussed by Labour MPs as potential candidates to replace Sir Keir include Home Secretary Shabana Mahmood. There is also speculation Energy Secretary Ed Miliband could stand.

The health secretary had a chance to respond to the claims when he was doing media interviews on Wednesday morning.

Speaking to the BBC, he said he was “not challenging the prime minister” adding: “I’m not doing any of the things some silly briefer said overnight.”

Asked if he could consider standing against the PM in the future, he replied: “I cannot see circumstances in which I would do that to our prime minister.”

He said the briefings to the media demonstrated that the culture in Downing Street was “toxic”.

He suggested he did not believe the prime minister had approved the briefing, telling the BBC: “I can tell you without having even spoken to the PM what he thinks of the briefings – the words he would use are not suitable for a family show like this.”

Despite winning a landslide majority in the July 2024 general election, Sir Keir has had a rocky time in Downing Street and opinion polls suggest he is unpopular.

Both the Budget in two weeks’ time, and elections in Scotland and Wales and local elections in England next year, are crunch points for the government.

Supporters of the prime minister have argued a leadership contest would plunge the party into the chaos associated with the last years of the previous Conservative administration.

In order to trigger a leadership contest against the prime minister, challengers would need the support of 20% of Labour MPs, which currently means 81 nominations would be required.

Some Labour MPs and ministers have publicly and privately condemned the briefings.

Appearing on BBC Politics Live, Business Minister Sir Chris Bryant said he thought they were “plain daft”.

Labour MP for Bassetlaw Jo White said: “This is a group of people who think they’re much cleverer than the rest of us, who spend their time selectively briefing journalists and stirring the pot.

“I want to simply say: we’re not having it.”

But some Labour MPs who are usually supportive of the prime minister described the timing and substance of the briefing as “badly handled” and “baffling”.

One senior Labour figure questioned why Sir Keir’s allies had “legitimised what was a taboo” by publicly entertaining the prospect of a leadership challenge.