Explained: How the UK Changes Prime Ministers — How Labour Elects a New Leader and Why Andy Burnham Is the Frontrunner

Labour Party MPs have started the nomination process for the next party leader to succeed Sir Keir Starmer, who has resigned. Andy Burnham is currently the only MP to have publicly declared his intention to run, and he is widely expected to become Prime Minister later this month. This means that the former Mayor of Greater Manchester could move into Downing Street just weeks after returning to Parliament via a by-election in Makerfield.

What happens next? According to Labour Party rules, MPs in the House of Commons can seek the required nominations to qualify as candidates during a one-week window from 9 to 15 July. Leadership candidates must secure nominations from 20% of Labour MPs. With 403 Labour MPs currently in office, this means 81 nominations are required.

Candidates must also receive nominations from at least three of Labour’s 31 affiliated socialist societies and trade unions, or obtain endorsements from 5% of Constituency Labour Parties (CLPs). Nominations from affiliated organisations must represent at least 5% of Labour’s affiliated membership and include two trade unions. Eligible unions include GMB, Unite, and Unison.

On 13 July, candidates will attend a parliamentary Labour Party hustings to answer questions from Labour MPs. If Burnham remains the only candidate, he may effectively speak at the hustings alone.

The nomination process for affiliated organisations begins at 18:00 BST (17:00 GMT) on 15 July and closes at the same time the following day. If necessary, the CLP nomination stage will run from 20 to 31 July.

What if Burnham is the only candidate? This is the most likely scenario — no other MP is currently seen as a credible challenger, and most MPs believe Burnham will become the next Prime Minister.

Wes Streeting, former Health Secretary under the Starmer government, was previously considered the most likely MP to announce a candidacy. However, shortly after Starmer’s resignation, the situation changed. Streeting publicly endorsed Burnham and suggested he would not run for leader.

If Burnham secures 323 nominations, mathematically no other candidate could reach the 81-MP threshold. If no other MP challenges him, Burnham could become Labour leader as early as 17 July. However, he will not formally become Prime Minister until three days later.

This is because Starmer must travel to Buckingham Palace to formally tender his resignation to King Charles III, after which the King will invite Burnham to form a new government. Since the leadership result is announced on a Friday, this formal handover will take place on the next working day — Monday, 20 July.

What if another candidate enters the race? If another MP joins the contest, the Labour leadership election will proceed from 16 July during the parliamentary summer recess. Starmer will remain Prime Minister until Parliament reconvenes on 1 September.

In this case, Labour members and affiliated trade union supporters will vote between 6 and 27 August to determine the winner. The result will be announced on 29 August.

Could a general election be held? Burnham has ruled out calling an immediate general election upon becoming Prime Minister. Last week, he stated in an online forum: “I will govern according to the 2024 manifesto.”

By September, the UK could have had seven Prime Ministers within a decade. Four of them took office mid-term without winning a general election: Theresa May in 2016, Boris Johnson in 2019, and Liz Truss and Rishi Sunak in 2022.

In each case, the opposition questioned their legitimacy. However, like his predecessor, the next Prime Minister is not obligated to call a general election before the current Parliament’s term ends in 2029.

Under the current system, voters elect MPs and parties, and those MPs and parties then select the party leader. The last general election was held on 4 July 2024, when Labour won a landslide majority. Therefore, legally, the next general election must be held by August 2029, but the Prime Minister has the authority to call an early election at any time before then.

Whether the Prime Minister calls an early election depends on several factors, including the governing party’s performance in opinion polls and whether the Prime Minister wants to seek renewed public mandate to advance their policy agenda. Thus, while Burnham has ruled out an immediate election, one could still occur before 2029.