By announcing his decision to resign as leader of the Labour Party on 22 June, Keir Starmer immediately set a leadership contest in motion. The catalyst for Starmer’s departure was Andy Burnham’s return to the Commons, after his impressive victory at the Makerfield by-election, and the ex-Greater Manchester mayor’s declared aim of challenging Starmer for the party leadership. So how does a Labour Party leadership contest play out?

How long is a Labour leadership contest?

According to the Labour Party’s rules, once a party leader resigns, the contest to find their successor begins automatically within an official outlined timeframe. The precise timings are determined by Labour’s National Executive Committee (NEC), a body composed of elected and nominated representatives from the party’s assorted affiliates and groups. In this particular case, following Starmer’s resignation statement, on 25 June the NEC announced its intention to receive nominations for the vacant leader’s post between 9 and 16 July. If one person was the only nominated candidate during this period, they would become party leader and PM-in-waiting on 17 July as there were no other challengers. However, if several candidates were nominated, then a balloting process (see below) was scheduled to take place from 6-27 August to determine the winner. The new leader would then be announced on 29 August at a special conference, just before parliament reconvenes on 1 September.

How is a new Labour leader appointed?

In order to be formally accepted as candidates in the contest, Labour leadership contenders have to be Labour MPs and nominated by

• 20 percent of Labour MPs (currently 81 of the 403 Labour MPs holding the whip)
• 3 or more affiliates (at least 2 must be trade unions) representing at least 5 percent of the affiliated membership OR at least 5 percent of constituency parties

In the current contest, Labour MPs submitted their nominations (9-15 July) followed by affiliates (15-16 July). If a candidate secured enough MP nominations but their affiliate nominations fell short, only then would constituency parties make nominations (20-31 July). Should only one candidate reach the nomination threshold, that individual would automatically become the party leader. By the close of nominations on 15 July, Burnham had received the official backing of 379 Labour MPs (94 percent), making it impossible for any other candidate to reach the 20 percent threshold. He was therefore declared the winner and became the new Labour leader on 17 July.

However, if more than one candidate had secured enough nominations, then the contest would have continued with a voting process, involving two groups (1) party members and (2) opted-in affiliated members of the party from affiliated organisations, such as the trade unions. Labour MPs would also have had one vote each and, as a result, would have been significantly outnumbered by these two voting groups.

Since 2015, Labour leadership contests have used a one-person-one-vote process to prevent dual voting by individuals who happen to be both party members and affiliate members. An alternative vote or preferential ballot system (sometimes known as instant run-off) is employed to determine the winner. If a candidate gets over 50 percent of the vote, they become the Labour leader. However, if no candidate achieves this level of support, then the lowest placed candidate is eliminated from the contest and their votes are redistributed to the voters’ second preference candidates. This elimination-redistribution process continues until a candidate emerges with over 50 percent of the vote. The process is basically the same if a Labour MP mounts a leadership challenge (which must be backed by 20 percent of their party colleagues in the Commons). Only the resignation of a Labour leader or the emergence of a challenger backed by 20 percent of Labour MPs can trigger a leadership election. In the latter scenario, the incumbent leader is automatically put on the ballot (unless they step down) and do not need to seek nominations. Labour MPs cannot hold a formal vote of no confidence in their leader. If the party leader resigns when Labour is in opposition, then the deputy leader takes over as leader and the NEC decides whether to hold a leadership contest immediately or wait until the period just before the annual party conference so the new leader is in place for that gathering. Deputy leader Harriet Harman, for instance, became party leader in 2010 between the departure of Gordon Brown and the election of Ed Miliband. Similarly, deputy leader Margaret Beckett took over the leadership between John Smith’s death and Tony Blair’s appointment as leader in 1994.

Recent changes to the leadership contest procedure

Prior to Labour’s October 2021 party conference (1) candidates needed to be nominated by 10 percent of the combined number of Labour MPs and MEPs (until the UK’s departure from the EU) and (2) ‘registered supporters’ could vote in leadership contests without becoming full party members. At that conference, the requirement to secure the support of 20 percent of MPs was introduced and registered supporter voting was abolished. The current rules concerning affiliate and constituency nominations date from 2018 but both groups played a voting role in the leadership contest before then.

When the party leader is the prime minister

Party leader and prime minster are distinct roles but they are obviously connected when one individual, such as Starmer, occupies both positions. Generally speaking, the PM is also the leader of their party because this is regarded as demonstrating their ability to retain their colleagues’ confidence in the Commons. When a party leader who is also PM resigns, it is customary for that person to stay on as premier until a new leader is announced at the end of the leadership contest. Recent Tory PMs, such as Cameron, May and Johnson, remained in office until a new Conservative leader had been selected. On May 10 2007, Tony Blair publicly stated his decision to resign as party leader and PM, but Gordon Brown, his uncontested successor, only replaced Blair as leader on 24 June and PM on 27 June.

Is a general election required once a new party leader assumes the premiership?

The short answer is no because only the PM has the ability to request a dissolution of parliament and call a general election. Ultimately, therefore, it will be up to the new leader of the Labour Party, Andy Burnham, as PM, to make a decision on whether or not to go to the polls shortly after taking office. There is no official requirement to hold a general election in the UK before August 2029. Historically, new party leaders who assume the premiership during the life of a parliament tend to avoid snap general elections immediately after taking office – as the examples of James Callaghan, John Major, Gordon Brown and Rishi Sunak all illustrate