Keir Starmer’s leadership appeared to be in crisis on Sunday following the departure of his key aide amid the fallout from the Mandelson controversy.

Downing Street’s chief of staff, Morgan McSweeney, resigned over his involvement in the ill-fated appointment of Peter Mandelson as the ambassador to the United States.

McSweeney admitted full responsibility for the choice to send the controversial peer to Washington, despite being aware of Mandelson’s past association with Jeffrey Epstein, even after Epstein’s conviction for child-sex crimes.

Meanwhile, Labour MPs are questioning how long Starmer can sustain his leadership without McSweeney, who was instrumental in Starmer’s ascent and regarded as the strategic force behind his decisions.

Critics on the left are calling for Starmer’s resignation, with former campaign strategist Jon Trickett asserting, “The responsibility lies at the top.”

Brian Leishman, Labour MP for Alloa and Grangemouth, echoed these sentiments, insisting, “A shift in political direction is necessary, and it must originate from the leadership.”

‘So the Prime Minister must look at his own position and question whether he should follow McSweeney’s lead one last time, and resign for the good of the country and the Labour Party.’

Liverpool MP Kim Johnson said the PM’s position was ‘untenable’, while York MP Rachael Maskell described Mr McSweeney’s departure as ‘a start’.

Keir Starmer’s premiership was in freefall on Sunday after his right-hand man walked the plank over the Mandelson scandal (Pictured: The Prime Minister on January 27, 2026)

Downing Street chief of staff Morgan McSweeney quit over his part in the disastrous appointment of Peter Mandelson as US ambassador (Pictured: McSweeney and Starmer on Sunday)

Mandelson was sacked last week amid revelations about his friendship with paedophile financier Jeffrey Epstein (Pictured: Mandelson on June 18, 2025, in London)

Last night, Sir Keir was drawing up plans for an emergency address to the nation to set out plans to clean up politics – and to signal to the public and financial markets that he is not on the brink of quitting. Sources said the Government’s policy agenda ‘has not changed’. The PM is also expected to address MPs at a meeting of the Parliamentary Labour Party today.

Leadership rivals including Angela Rayner and Health Secretary Wes Streeting were last night jockeying for position in a potential leadership contest.

Deputy Prime Minister David Lammy also appeared to be eyeing his chances as he let it be known that he advised the PM against appointing Mandelson. Energy Secretary Ed Miliband is being talked up as a potential ‘king-maker’ in any contest, with some allies suggesting he could even run himself, despite being roundly rejected by the public a decade ago.

Sir Keir’s dwindling band of allies warned that forcing out the PM just 18 months after Labour’s landslide win could tip both the party and country into turmoil. Work and Pensions Secretary Pat McFadden said ditching the PM would cause ‘chaos and uncertainty – economically, politically and reputationally around the world’.

Kemi Badenoch welcomed Mr McSweeney’s resignation, saying it was ‘about time’. But the Tory leader said the PM ultimately had to ‘take responsibility’ for agreeing an appointment that has triggered a wave of public revulsion.

In a post on X, she said: ‘Once again with this PM it’s somebody else’s fault: “Mandelson lied to me” or “Morgan advised me”. Keir Starmer has to take responsibility for his own terrible decisions. But he never does.’

Mr McSweeney is the second chief of staff to depart during Sir Keir’s turbulent reign, following the sacking of Sue Gray just months after the 2024 election.

Labour calls have mounted for his resignation in recent days following the release of emails by the US Department of Justice suggesting that Mandelson leaked ‘market-sensitive’ information to Epstein while serving as business secretary. Sir Keir last week said he had ‘full confidence’ in his chief of staff, telling MPs: ‘He’s an essential part of my team.’

In a resignation statement, Mr McSweeney said: ‘The decision to appoint Peter Mandelson was wrong. He has damaged our party, our country and trust in politics itself.’ In a swipe at Whitehall and the security services, Mr McSweeney said the vetting system for appointments had to be ‘fundamentally overhauled’.

Friends of Mr McSweeney said the PM had made a disastrous decision in letting him go. One source said it was like ‘breaking the legs of your star striker’ (Pictured: McSweeney at Downing Street on 10 October, 2024)

Mr McSweeney’s deputies Jill Cuthbertson and Vidhya Alakeson will step up as joint ‘acting chiefs of staff’ in the short term.

Friends of Mr McSweeney said the PM had made a disastrous decision in letting him go. One source said it was like ‘breaking the legs of your star striker’, adding: ‘We will all have to see if Keir can survive alone.’

A Labour MP told the House magazine that Mr McSweeney’s departure would trigger a lurch to the Left and leave the party moving ‘full speed ahead to uber-woke, net-zeroist, rejoinerism’. Supporters of Ms Rayner and Mr Streeting traded blows yesterday as the prospects of an imminent leadership race intensified.

An ally of Mr Streeting pointed to Ms Rayner’s unresolved dispute with HMRC over unpaid stamp duty on her luxury second home, adding: ‘It’s a very hard pitch to suggest you want to replace one scandal-ridden leader with another.’

But an ally of Ms Rayner suggested the Health Secretary would be undone by his past friendship with Lord Mandelson.