How quickly could Andy Burnham become the UK’s prime minister?

Those who don’t pay much attention to politics could be forgiven for not being fully on top of this, but 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 go in a particular way. And there are plenty of alternate outcomes.

Slightly slower: Burnham in No 10 within weeks

This is largely a re-run of the scenario above, but with the difference that Starmer agrees a timetable to depart which takes slightly longer, perhaps including a final diplomatic mission to the Nato summit in Ankara in early July.

Without a full contest taking place, Burnham and his advisers might be sanguine about this, within reason – he would most likely wish to take over before parliament goes into recess later in July.

It is worth noting at this point that Starmer has repeatedly ruled out stepping aside, saying he would fight any contest. This resolve might, however, be swayed by either very obvious mass support for Burnham among Labour MPs, or large numbers of cabinet ministers threatening mutiny.

It is also contingent on no other challengers coming forward, most notably Wes Streeting. The health secretary has said he will launch a challenge and has enough MP backers, even if the latter remains to be seen.

Quite a bit slower: a full contest

If Starmer, Streeting or anyone else decides to fight Burnham for the leadership, and they get the sufficient suite of nominations, it will go to a vote of Labour’s membership. The timetable will necessarily be longer, but how much longer depends.

The timetable is set by the NEC, which has some leeway. In 2020, when Labour was in opposition and had just lost the December 2019 election, it set aside three months for the contest which saw Starmer take over as leader.

But in September 2025, with Labour in government and Angela Rayner having resigned as deputy leader, the contest to find her replacement – held under the identical rules – was accelerated, taking about six and a half weeks.

Choosing a new prime minister is, of course, even more urgent, and so the timetable could be compressed more, although Labour officials will want to ensure there is time for candidates to get a proper hearing.