Guest post by Andreas Murr, CIDE and University of Warwick. 1 July 2024

Voters will choose the next British prime minister this Thursday 4th July 2024.  The political parties narrowed down this choice much earlier.  The Labour party chose Keir Starmer as their leader on 4 April 2020; the Conservative party chose Rishi Sunak as their leader on 24 October 2022.  One of them will be the next prime minister.  Does their selection as party leaders tell us anything about who will be selected as prime minister?

The Party Leadership Model argues that it does (see here and here).  The argument is that party leadership contests predict general elections because MPs have both the knowledge and a strong incentive to pick a party leader who has the best chance of winning the general election.  Hence the party leader who performs better in the leadership contests has a greater chance of also performing better in the general election.

Consider the 2019 general election.  Boris Johnson beat Jeremy Hunt by a margin of 26.5 percentage points among Conservative MPs, while Jeremy Corbyn lost to Andy Burnham by 13.9 points among Labour MPs – though Corbyn was later selected by party members as the leader.  Since Johnson’s margin of victory among his own MPs was larger than Corbyn’s the model predicted correctly a Conservative victory for 2019.  Overall, eleven out of fourteen past elections since 1966 were won by the party leader with the larger margin of victory among MPs.

What does the model predict for the 2024 election?  

In the 2020 Labour leadership contest, Keir Starmer beat Rebecca Long-Bailey by a margin of 25.9 percentage points among Labour MPs.  In the 2022 Conservative leadership contest, Rishi Sunak beat Liz Truss by a margin of 6.7 points among Conservative MPs – though Truss was later selected by party members as the leader.  After six tumultuous weeks as prime minister Truss resigned and Sunak was selected unopposed as party leader and, consequently, prime minister in October 2022. Hence the best measure of Sunak’s performance remains the leadership contest in July 2022.

This means that the Party Leadership Model still makes the same forecast as it did on 30 September 2022: Starmer will win the Prime Ministership.  Due to its simple specification, the model is always very cautious in its seat share predictions.  The model forecasts Starmer to win 51.5% of the seats, and Sunak 41.4%.  Of course, given that the model is based on only 14 elections, these forecasts come with uncertainty.  Soon we will know how accurate they were.