What happens if UK's Starmer quits, or is challenged?

Starmer faces calls to quit as team reels from Mandelson ambassador appointment

Britain's Prime Minister Keir Starmer answers the Prime Minister's Questions at the House of Commons in London, Britain Feb 4, 2026. © House of Commons/Handout via REUTERS

Prime Minister Keir Starmer is facing calls to step down with his team in crisis over the appointment of Peter Mandelson as ambassador to the US - a decision that has backfired following revelations about the depth of Mandelson's relationship with US sex offender Jeffrey Epstein.

Here's what happens if Starmer resigns or faces a leadership challenge:

WHAT IF STARMER RESIGNS?

The party would hold a leadership contest to replace him.

Any candidate wishing to stand would need to secure the support of 20 percent of Labour members of parliament. With Labour currently holding 404 seats, that equates to 81 backers.

Candidates also must meet thresholds for support from grassroots Labour Party organisations, and from affiliated organisations such as trade unions.

If only one candidate qualifies, there is no vote: the candidate is elected unopposed as Labour leader and becomes prime minister.

If more than one candidate qualifies, the winner is decided by a ballot of Labour members and affiliates. The winner then becomes prime minister.

HOW CAN STARMER'S LEADERSHIP BE CHALLENGED?

A leadership challenge can be triggered if there is enough support behind a candidate to replace Starmer.

Candidates to replace the prime minister would need to meet the 81 lawmaker threshold, as things currently stand. Starmer would automatically be on the ballot paper in any such contest.

The contest would then be run according to the same process that would follow a resignation.

It is generally harder for Labour lawmakers to remove a prime minister than the rival Conservative Party, which went through five prime ministers in eight years from 2016, because the Labour rebels have to rally behind specific candidates, rather than just a 'no confidence' in the leader.

Labour members of parliament have never successfully removed a sitting prime minister in the party's more than 125-year history.

Former Prime Minister Tony Blair set a deadline for his departure after some junior members of his government resigned in 2006, but he did not quit immediately.