If Starmer, Streeting, or anyone else decides to challenge Andy Burnham for the leadership and secures the necessary nominations, the decision will go to a vote of Labour's membership. Burnham, the Greater Manchester mayor, is currently running in the Makerfield byelection.
Explainer: How Quickly Could Andy Burnham Become the UK's Prime Minister?
If he wins the Makerfield byelection, the Greater Manchester mayor faces several scenarios in his bid to replace Keir Starmer. Those not closely following politics might be surprised to learn that the UK could have a new prime minister soon—potentially within weeks.
So how quickly could Andy Burnham replace Keir Starmer if Burnham wins Thursday's Makerfield byelection? Actually, quite quickly, but only if events unfold in a specific way. There are also plenty of alternate outcomes.
The Fastest: Burnham in No 10 Within Days
Labour's rulebook states that an MP challenging a sitting party leader must be nominated by at least 20% of the parliamentary party (currently 81 MPs), as well as by at least 5% of all local branches or at least three party-affiliated groups, of which a minimum of two must be unions. Any contenders meeting the threshold proceed to a vote of party members, assuming there is more than one challenger. If a sitting leader is challenged, they do not need to meet these requirements and are automatically included in the members' vote if they choose to participate.
In one scenario, Burnham is elected as Makerfield's MP, Starmer decides to step down immediately—perhaps after a mass of senior cabinet ministers threaten resignation—and no other challengers come forward. Burnham would still need formal support from MPs and party groups, but with a coronation looming, this would likely be swift. Labour's National Executive Committee (NEC) would set a timetable, and without a membership vote, the process could be completed in days.
Slightly Slower: Burnham in No 10 Within Weeks
This scenario largely mirrors the above, but with Starmer agreeing to a slightly longer departure timetable, perhaps including a final diplomatic mission to the NATO summit in Ankara in early July. Without a full contest, Burnham and his advisers might be comfortable with this, as he would likely wish to take over before parliament's recess later in July. However, Starmer has repeatedly ruled out stepping aside, saying he would fight any contest. His resolve might waver if there is obvious mass support for Burnham among Labour MPs or large numbers of cabinet ministers threatening mutiny. This scenario also depends on no other challengers coming forward, most notably Wes Streeting, who has said he will launch a challenge and claims sufficient MP backers.
Quite a Bit Slower: A Full Contest
If Starmer, Streeting, or anyone else decides to fight Burnham for the leadership and secures the necessary nominations, the decision goes to a vote of Labour's membership. The timetable, set by the NEC, will necessarily be longer, but the exact duration depends on circumstances. In 2020, when Labour was in opposition after losing the December 2019 election, the NEC set aside three months for the contest that saw Starmer become leader. However, in September 2025, with Labour in government and Angela Rayner having resigned as deputy leader, the contest to find her replacement—held under identical rules—was accelerated to about six and a half weeks. Choosing a new prime minister is even more urgent, so the timetable could be compressed further, though Labour officials will want to ensure candidates have time for a proper hearing.
