The resignation of the prime minister's chief of staff comes just days after Starmer described McSweeney as "an essential part of my team".

He was responding at Prime Minister's Questions after Badenoch said Starmer had chosen "to inject Mandelson’s poison into the heart of his government on the advice of Morgan McSweeney", and asked if the PM still had confidence in his adviser.

"He helped me change the Labour Party and win an election. Of course, I have confidence," Starmer told the House of Commons in defence of his top adviser.

Like previous advisers in Downing Street, such as Dominic Cummings or Alastair Campbell, McSweeney has come under scrutiny, but Starmer has consistently stood by him.

During a row late last year over whether McSweeney was linked to anonymous briefings against Labour cabinet ministers, one ally of the prime minister told the BBC: "They are coming for Morgan because they want to get Keir."

A gift for opposition parties, as Labour insiders wonder who fills the role nextpublished at 15:57 GMT

15:57 GMT

Laura Kuenssberg
Presenter, Sunday with Laura Kuenssberg

The next couple of days could be pretty brutal for the Labour Party, with rows over whose fault Mandelson's appointment really was.

McSweeney's taken the fall. But what about the PM's own role? What about Jonathan Powell, the national security adviser? Many in Labour had long been unhappy at way they thought McSweeney ran No 10. They often laid policy decisions, mishaps and mistakes at his door. The truth is he'd had a target on his back for many months.

A McSweeney ally tells me it's "absurd that he has resigned over a bit of advice when there were people who have known Peter for decades pushing for his hiring and are now pretending it was nothing to do with them."

Some Labour MPs are hailing McSweeney departure - Richard Burgon, on the left of the party, says it's an "important first step".

The argument in party will run over whether it was inevitable, right, or wrong.

What's definitely clear is it's a gift for the opposition parties, and chucking chiefs of staff over the side rarely solves big longer term problems for any leader.

In the meantime, Labour insiders are scratching their heads over who will take the job of Starmer's chief of staff next.

We can bring you some reaction to McSweeney's departure from opposition parties:

• Liberal Democrat deputy leader Daisy Cooper says the PM "can change his advisers all he likes, but the buck stops with him"
• Green Party leader Zack Polanski describes McSweeney's departure as "necessary but not sufficient". Writing on X, he adds: "He [Starmer] knew. And still appointed him [Mandelson]. Starmer needs to go"
• Robert Jenrick, who recently defected from the Tories to Reform, says: "We’re in a real mess and things need turning around. Instead this Labour government is talking about Peter Mandelson"

As a reminder: We also brought you Keir Starmer and Kemi Badenoch's reactions a little earlier.

The question now is if this resignation takes the heat off Starmerpublished at 15:39 GMT

15:39 GMT

Chris Mason
Political editor

McSweeney has long been seen as the genius of the remoulding or rebirth, as some saw it, of the Labour Party and had campaigned to change it into one that would be electable again. He has been largely credited with Labour's subsequent landslide victory in the last election.

There has been a lot of pressure on the former chief of staff for some time - he is somewhat of a lightning rod. McSweeney acknowledges that he was central to Mandelson's appointment - a move which has since caused PM biggest crisis of his premiereship.

The big question now is whether McSweeney's departure takes the heat off this political row. Or, does it remove the very lightning rod McSweeney has been and hit the PM directly?

It is worth reflecting that at the time of Mandelson's appointment, many people thought it was a good appointment, given the need for someone with savvy diplomacy in Washington following Trump's return to office - and early evidence suggested Mandelson was doing a good job.

However, the extraordinary revelations that have emerged obviously changed the picture.

Despite Starmer's landslide majority in his election win, he has been overshadowed by turbulence in Downing Street.

It's worth reminding ourselves this is a new-ish government, but the turbulence we've seen around it is the sort of thing you'd associate with the tail end of a PM's time.

Morgan McSweeney was the PM's "closest aide", says our political correspondent Billy Kenber, and a "hugely significant figure" in the Starmer project.

He was there when Starmer became party leader, and has overseen the reshaping of the Labour Party under Starmer's leadership.

McSweeney has been central to Starmer's operationpublished at 15:22 GMT

15:22 GMT

Paul Seddon
Political reporter

Morgan McSweeney has sought to keep a low profile in public, and until relatively recently there have been relatively few pictures of him in circulation.

But he is absolutely central to the Starmer project, and the way the prime minister’s Downing Street operation works.

He began his career trying to regain control of the local party from the hard left in Lambeth, south London, and then set up a think tank opposed to the party’s leftward turn under Jeremy Corbyn.

He ran Starmer’s successful bid for the Labour leadership in 2020, and was the party’s campaign director for the 2024 general election before taking over the chief of staff role after the departure of Sue Gray.

He is thought to have been instrumental in pushing Starmer to take a tougher line on immigration and crime, as part of a strategy to broaden the party’s appeal after its crushing defeat at the 2019 election.

But his commanding position within Starmer’s Downing Street has long made him a bogeyman for backbenchers on the left of the party.

Starmer relied on McSweeney's instincts - so what now?published at 15:15 GMT

15:15 GMT

Laura Kuenssberg
Presenter, Sunday with Laura Kuenssberg

Prime Minister Keir Starmer "is facing into the storm as the most talented campaigner in modern politics leaves his team. He would not be PM without Morgan, I wonder if he'll be PM for much longer now", a Labour source says.

There'll be an enormous number of chats about McSweeney's exit in the next couple of days - but this really is important beyond the soap opera, for four big reasons.

For one, the PM really, really relied on McSweeney's political instincts - much, much more than Boris Johnson on Dominic Cummings, Theresa May on Gavin Barwell, or David Cameron on Edward Llewellyn.

Second, McSweeney knew how to win and was central to rebuilding Labour after the party was hammered in 2019. Third, losing a vital ally shows how deep Starmer's problems run - McSweeney was one of the PM's last plays to hold his critics at bay.

Finally, don't underestimate the disruption of changes like this, especially when the government is already struggling. Starmer's critics have a scalp, so what now?

Even the final decision for him to quit is causing turmoil.

Just before we went on air at 09:00 this morning, two sources told us that this was not the plan and nothing was changing - and senior minister Pat McFadden even said there’d be "no point" getting rid of him, on air.

Even cabinet ministers have been shocked by this afternoon’s decision and assumed, as McFadden suggested this morning, that it was not going to happen.

On Sunday with Laura Kuenssberg this morning, Work and Pensions Secretary Pat McFadden said there was "no point... whatsoever" in getting rid of Morgan McSweeney because of the fallout from Peter Mandelson's appointment.

He told the programme: "I do think he should think he should carry on, I do think he should keep delivering.

"And I know that when it's a rough week it's easy to reach for a lever, change the leader, change the leader's chief of staff and think that will fix it."

Image source, PA Media

On social media, Conservative Party leader Kemi Badenoch has said that "it's about time" for McSweeney to resign.

She has criticised Starmer, arguing that "once again with this PM it’s somebody else’s fault: 'Mandelson lied to me' or 'Morgan advised me'."

Badenoch adds that the PM needs to "take responsibility for his own terrible decisions".

Chris Mason
Political editor

"It’s been an honour working with Morgan McSweeney for many years," Prime Minister Keir Starmer says.

"He turned our party around after one of its worst ever defeats and played a central role running our election campaign. It is largely thanks to his dedication, loyalty and leadership that we won a landslide majority and have the chance to change the country.

"Having worked closely with Morgan in opposition and in government, I have seen every day his commitment to the Labour Party and to our country. Our party and I owe him a debt of gratitude, and I thank him for his service."

How much power does the chief of staff have?

The chief of staff is one of the government's most powerful roles. Its holder is politically and personally close to the prime minister.

The responsibilities of the post vary widely, but can include:

• Advising the prime minster on government policy, party politics and communication strategies
• Overseeing and managing Downing Street political staff and the work of special advisers
• "Gatekeeping": sitting outside the prime minister's office and controlling who gets in and who doesn't
• Seeing what the prime minister sees, and accompanying the PM to meetings

Image source, PA Media

McSweeney was born in Ireland but moved to London as a teenager, joining the Labour Party in a junior role under Tony Blair. He later worked for housing secretary Steve Reed.

He has been described as quiet, unassuming, and even shy, particularly in public.

But he went on to mastermind Labour's landslide 2024 general election victory, and then became Starmer's chief of staff after the dramatic resignation of Sue Gray.

As chief of staff, he had one of the most powerful roles in government, which included advising the prime minister on government policy, party politics and communication strategies.

• You can read more about his career here

There had been calls in recent days for McSweeney to be sacked over the Mandelson scandal.

McSweeney is often referred to as Mandelson's protege.

A number of Labour MPs have wanted McSweeney out for some time.

Labour MPs who have called for his departure include Clive Efford, Patrick Hurley and Kim Johnson. Labour's former deputy leader Harriet Harman has also said the PM should consider "a real reset" in Downing Street.

Earlier in the week, the PM's official spokesperson said he had "full confidence" in McSweeney.

We can now bring you Morgan McSweeney's statement announcing his resignation.

"After careful reflection, I have decided to resign from the government.

"The decision to appoint Peter Mandelson was wrong. He has damaged our party, our country and trust in politics itself.

"When asked, I advised the Prime Minister to make that appointment and I take full responsibility for that advice. In public life responsibility must be owned when it matters most, not just when it is most convenient. In these circumstances, the only honourable course is to step aside.

"This has not been an easy decision. Much has been written and said about me over the years but my motivations have always been simple: I have worked every day to elect and support a government that puts the lives of ordinary people first and leads us to a better future for our great country.

"Only a Labour government will do that. I leave with pride in all we have achieved mixed with regret at the circumstances of my departure. But I have always believed there are moments when you must accept your responsibility and step aside for the bigger cause.

"As I leave I have two further reflections:

"Firstly, and most importantly, we must remember the women and girls whose lives were ruined by Jeffrey Epstein and whose voices went unheard for far too long.

"Secondly, while I did not oversee the due diligence and vetting process, I believe that process must now be fundamentally overhauled. This cannot simply be a gesture but a safeguard for the future.

"I remain fully supportive of the Prime Minister. He is working every day to rebuild trust, restore standards and serve the country. I will continue to back that mission in whatever way I can. It has been the honour of my life to serve."

We've just learnt that Keir Starmer's chief of staff Morgan McSweeney has resigned.

"After careful reflection, I have decided to resign from the government. The decision to appoint Peter Mandelson was wrong. He has damaged our party, our country and trust in politics itself," he says in a statement.

This story is developing. We'll bring you more in just a moment.