Sir John Curtice: Understanding the exit poll numbers

Written by Sir John Curtice, a specialist in polling data for the BBC.

Labour is on track to win by a large margin as expected, but they may not have quite reached the same level of success as Tony Blair did in the 1997 general election when it comes to securing a majority.

They might have accomplished this with a smaller portion of the vote compared to what former leader Jeremy Corbyn received in 2017.

The Conservative party may see their lowest share of the vote and number of seats ever. This could be due to their vote decreasing in areas where they traditionally had more support, as Reform's popularity has grown in those regions.

In addition to the difficulties facing the Conservatives, Labour is gaining more support in areas where they were previously in second place. At the same time, the Liberal Democrats are seeing success in areas where they were also in second place to the Conservatives, especially in seats they previously held before 2015.

It is these trends that, most importantly, help clarify why the number of Conservative seats is predicted to be so small.

Professor John Curtice on predictions for Reform UK and the SNP

The Conservative party seems to have faced significant losses in areas where over a third of households are paying off a mortgage. This could be a result of the negative impacts of the previous prime minister Liz Truss's economic policies.

Reform UK seems to be performing better than predicted in the polls. This is mainly because the Conservative party has seen a decrease in votes in areas they used to dominate, and also because Reform UK has made significant progress in areas where the majority of people voted for Brexit in 2016. This is particularly evident in constituencies where the Conservatives are currently in power.

Changes are steadily increasing in areas where the Conservatives were victorious in 2017 but where the Brexit Party did not compete in 2019.

Yet, there is a great deal of uncertainty surrounding how many seats Reform will secure.

Our analysis indicates that there are numerous locations where they have a slight possibility of winning.

More Votes For Labour Where Health Is Poor

On the other hand, the Labour party has seen an increase in their vote in areas where many residents report poor health, indicating a sense of inequality, and in regions that had a higher percentage of voters choose to leave the EU in 2016. Additionally, the party is gaining momentum in Scotland but facing challenges in Wales, despite holding power in the Senedd since 2021.

The Liberal Democrats are performing decently in areas where they are the second largest party behind the Tories. However, their support has decreased in constituencies where the Conservatives were being challenged by Labour.

They are also showing improvement in areas where there was a significant number of votes to leave, which was one of Ed Davey's goals.

The Green Party is doing very well in areas with a large number of young people. This could be one reason why the Labour Party may not get more than 40% of the votes in the upcoming election. Even though the Green Party has received its highest vote share ever in a general election, they may only win a few seats because their support is spread out evenly across the country.

Unanswered Questions In Scotland

In Scotland, it seems like the SNP did not do as well as expected in the recent election. However, the decrease in support for the party seems to be smaller in areas where more people consider themselves Scottish rather than British.

The survey data in Scotland is based on a limited number of sampling points. If the poll has slightly exaggerated Labour's lead over the SNP, the final results for the latter party could actually be higher.

The prediction for the SNP - and for Scotland overall, where the exit poll is indicating significant Labour advances - should be approached with a lot of care.