How EU policy can win the next general election

Executive Summary

This report assesses the impact of four hypothetical Labour policy positions on EU relations on Westminster voting intention, to estimate how Labour’s EU policy position might affect the outcome of a General Election. 

The four Labour policy positions on EU relations tested were: seeking a closer relationship with the EU without rejoining the Customs Union, Single Market or the EU itself; rejoining the Customs Union; rejoining the EU Single Market; rejoining the EU. The report also includes the results of a standard Westminster voting intention question. 

To carry out the assessment, Best for Britain asked YouGov to survey 13,433 people between 27th May – 11th June 2026, before Andy Burnham became leader of the Labour Party and UK Prime Minister. For each of the four Labour policy positions tested, and standard Westminster voting intention question, YouGov carried out a corresponding multilevel regression and post-stratification (MRP) analysis to estimate the vote shares of each Westminster party in the 632 parliamentary constituencies in Great Britain. 

The report builds on previous Best for Britain research assessing the impact of Labour’s EU policy position on EU relations on propensity to vote, and which EU relationship people wanted to see the UK Government propose.

The results in this report showed that the more ambitious Labour’s policy pitch on EU relations, the better the party’s electoral performance at the next General Election is likely to be. 

All EU relationship options beyond the UK Government’s current red lines were found to  increase Labour’s voting intention above Reform UK’s, rising to 37% of national vote share where Labour supported membership of the EU. Crucially, Labour moving to a more ambitious policy position did not result in an increase in support for Reform UK, or the Conservative Party. 

Best for Britain then used the YouGov projections and conducted further modelling and analysis. Our analysis of how Labour’s policy pitch on EU relations would affect seats won by Labour at the 2024 General Election showed that the more ambitious Labour was, the more constituencies it was likely to hold on to. EU membership was the only EU policy position which put Labour close to keeping a parliamentary majority, with the party estimated to hold on to 321 of the seats it won at the last election in this scenario  – just three short of a majority. 

Our analysis shows that the more ambitious Labour’s policy position on EU relations, the fewer seats it was estimated to lose to parties on both its left and right flanks across the whole of Great Britain. In seats where Labour is facing Reform UK, by appealing to left-of-centre voters, an ambitious EU policy allowed Labour to outpace Reform UK, winning more contests. In seats where Labour is facing parties on its left flank, again by appealing to left-of-centre voters, it was able to push challengers into second place. The effect was observed in all regions of England, but was most noticeable in Scotland and Wales, where Labour is facing a real possibility of being squeezed out of Westminster politics altogether. 

In Scotland, moving to a policy position of EU membership resulted in Labour retaining 32 seats, or 86% of the constituencies it won in 2024. In Wales, an election pledge to EU membership resulted in Labour retaining up to 25 of the 27 constituencies won at the last election. 

Labour moving to support a policy of either joining a Customs Union or the EU Single Market was found to substantially increase the party’s national vote share too, to 34% and 33% respectively. However, previous Best for Britain research found the Customs Union and Single Market policy proposals to be the least popular of any option for closer relations with the EU, even behind the UK Government’s current approach to EU relations within its 2024 manifesto red lines. As such, it was most likely that the positive performance of the policies was due to respondents being ‘squeezed’. That is to say that the draw of even these more modest Labour policy pitches on EU relations were enough to significantly shift voting patterns in Labour’s favour, despite people preferring EU membership.

However, neither a policy pledge to joining the Customs Union, or the EU Single Market, put Labour close to the seat haul necessary to form a majority government after the next General Election. Indeed, the results showed that a Labour-led coalition government would be the only likely electoral outcome of Labour pledging to join the Customs Union or Single Market. Furthermore, this was before consideration of how all other parties might react to Labour backing a Customs Union or the EU Single Market at an election, which was not captured by the data presented in this report. This would likely be a significant factor in Scotland and Wales, where the SNP and Plaid Cymru could simply outflank Labour by pitching a policy of full EU membership.

The impossibility of modelling how all other parties would react to Labour offering different policies on EU relations at the next election, the various combinations of reaction possible, and the practicalities of General Elections such as tactical voting, meant that the seat totals for the Liberal Democrats and the Green Party were ultimately unlikely to be reflected at an actual election event. Consequently, Best for Britain’s additional analysis sought to address this by using the YouGov projections and conducted further modelling and analysis to develop a scenario-based approach to estimate overall seat hauls for each of the scenarios modelled. The results, however, were the same. Labour maintaining its red lines on EU relations was estimated to result in Labour failing to hold on to enough seats to form a government – whether alone, or in coalition. Both the scenarios where Labour pledged to join a Customs Union or the EU Single Market were most likely to result in a Labour-led coalition government. The only scenario to place Labour close to obtaining a majority, was where it pledged to take the UK into the EU. In this scenario, Labour was estimated to win 321 seats – five short of a majority. 

Whichever way the data was analysed, more ambitious policy pitches by Labour worsened the electoral prospects of both the Conservative Party, and Reform UK. The more ambitious Labour’s pitch on EU relations, the more the Conservative Party was likely to be squeezed out of seat contests by both Reform UK on its right flank, and by the parties on its left flank. The more ambitious Labour’s policy position on EU relations, the fewer seats Reform UK was likely to win – because Labour successfully appealed to more left-of-centre voters in more constituencies, winning more contests against Reform UK in seats across Great Britain. 

As political parties start to shift their focus to the next UK General Election, the data in this report suggests that a commitment to EU membership in Labour’s next manifesto will be key to returning a Labour-led government, rather than a Reform UK-led one.

Headline Findings

1. All EU relationship options beyond the UK Government’s current red lines increased Labour’s voting intention above Reform UK’s, rising to 37% of national vote share where Labour supported membership of the EU. Labour moving to a more ambitious policy position did not result in an increase in support for Reform UK, or the Conservatives.
2. Where Labour pledged to support EU membership, the party was estimated to retain 323 seats of the 411 it won at the 2024 General Election, just three short of a majority. The more ambitious Labour’s policy position on EU relations, the more seats the party won in 2024 it was likely to hold on to, and the more likely Labour was to stay in power after the next election.
3. Labour moving to support a Customs Union, or membership of the EU Single Market, also resulted in substantial increases in Labour’s national vote share, estimated at 34% and 33% respectively. When it came to seat hauls however, neither supporting a Customs Union (288), or the Single Market (280), put Labour in range of retaining enough seats won in 2024 to form a majority government. Continuing to support its current red lines only resulted in Labour holding on to 190 seats won at the last election.
4. Labour moving to support EU membership was found to prevent Labour losing seats to parties on both its left and right flanks, and increase Labour’s seat haul in all regions of England, but especially in Scotland and Wales.
5. Even scenario-based analysis of seat marginality, as well as tactical voting showed that moving to a policy position of EU membership was the most likely EU policy to put Labour within touching distance of an overall parliamentary majority on Central seat estimates.

How Labour’s EU policy affects Labour voting intention

The results showed that an ambitious policy position on EU relations can substantially improve Labour voting intention. All EU relationship options beyond the UK Government’s current red lines increased Labour’s voting intention above Reform UK’s.

Labour moving to a policy of full EU membership resulted in the most significant increase in voting intention, rising to 11 percentage points clear of Reform UK.

In a scenario where Labour pledged full EU membership, Labour’s voting intention doubled compared to June 2026 (from 18% to 37%).

The results also showed significant jumps in Labour’s vote share in a scenario where it pledged to join the Customs Union (34%) and Single Market (33%).

How Labour’s EU policy affects Labour-held Seats

At the next general election, it was assumed that Labour would centre its focus on defending the seats it won at the 2024 election.

Therefore, MRP results were analysed by comparing what effect each of the polled EU policy positions had on seats won by Labour at the 2024 General Election.

The MRPs showed that the more ambitious Labour’s EU policy was, the more seats it was likely to hold onto, and the more likely Labour was to stay in power after the next election.

EU membership was the only EU policy position which put Labour close to obtaining a parliamentary majority.

In this scenario Labour was estimated to reach 323 seats, just three short of a majority.

The 323 seats included 251 that Labour won in 2024 and was estimated to hold by a margin of more than five percentage points, and a further 72 estimated to be held within the five percentage point margin.

Customs Union and Single Market

Under either scenario, Labour would be projected to hold onto more than 200 of its 2024 seats (216 for Customs Union, 215 for Single Market) by a margin of more than 5 percentage points. Under a Customs Union scenario, 72 further seats would be held marginally, with 65 seats held marginally if the party were to support Single Market membership.

Neither the Customs Union nor Single Market MRPs put Labour near the 326 mark needed for an overall majority. The best the party could realistically hope for in these scenarios was to try to form a coalition government.

Closer relations without joining the EU, Single Market or Customs Union

Labour’s 2024 general election manifesto stated there would be “no return to the single market, the customs union, or freedom of movement”. The data presented in this report clearly showed that going into the next election with the same ‘red lines’ was unlikely to be a sustainable political strategy.

Maintaining Labour’s red lines was estimated to result in Labour failing to hold on to enough seats to form a coalition government.

Scotland

Labour moving to a policy position of supporting EU membership was estimated to result in Labour winning 32 seats in Scotland, retaining 86% of the seats it won in 2024.

Wales

Results showed that in Wales, the greater Labour’s ambition on UK-EU relations, the more seats Labour was estimated to win. A Labour policy position of EU membership was most effective at reducing seat losses to both Reform UK and Plaid Cymru.

The North West

Labour adopting a policy position of EU membership was estimated to deliver the best result for the party. In this scenario Labour was estimated to hold onto 57 of the 65 seats it won in the North West in 2024, winning 44 of them by a margin of at least five percentage points.

East Midlands

In the scenario where Labour committed to EU membership, the party was estimated to win 20 seats in the East Midlands, retaining three more seats that it won in 2024 compared to the Single Market scenario, with one seat projected to be a tie.

The South West

The results showed that in the South West, the more ambitious Labour’s position on EU relations, the more of its 2024 seats it was likely to hold.  In the scenario where Labour supported EU membership, the party was estimated to retain 21 of the 24 seats won in 2024, with one seat a tie and just two expected losses to Reform UK.

Yorkshire and the Humber

In Yorkshire and the Humber, Labour was estimated to perform best in the scenario where the party adopted a policy of EU membership. Under this MRP scenario, the party was expected to retain 27 of the constituencies it won in the region in 2024.

Seats where Labour could advance

The MRP data also reveals a number of seats where Labour could advance on its 2024 position, through a combination of its pro-EU position drawing support from other parties, and the rise of Reform UK splitting the vote of the right bloc.

In the EU Membership MRP, there were 17 seats where Labour was estimated to win the seat by a margin of 10 percentage points or more. These included high-profile seats such as the Leader of the Opposition’s seat of North West Essex, and the Shadow Home Secretary’s seat of Croydon South.

How Labour’s EU policy would affect an Election: Customs Union or Single Market

Labour moving to support either a Customs Union or Single Market policy would likely increase its seat haul, compared to if it maintained its red lines on EU relations.

However neither policy put Labour close to the seat haul necessary to form a majority government after the next General Election.

This meant the Customs Union and Single Market policy positions would likely result in a Labour-led coalition government.

However, with even central estimates of both Customs Union and Single Market MRPs putting the Labour and Liberal Democrat combined seat haul only narrowly clear of the 326 mark necessary for a parliamentary majority, the results suggested that a three-party, rather than a two-party coalition would be a possible outcome.

The Customs Union and Single Market MRP central estimates also suggested that Reform UK and Conservatives would be less likely to gain enough seats to be able to form a government, even in a coalition.

How Labour’s EU policy would affect an Election: EU Membership

The EU membership MRP was the only one that estimated Labour’s seat haul to be within range of forming a majority government, with Central estimates showing Labour winning 321 seats – five short of a majority.

The results showed that the more ambitious Labour’s policy on EU relations, the better Labour’s estimated seat haul.

The results showed that Labour’s policy on EU relations could be the difference between a Labour-led government, and a Reform-led one.

Methodology

On behalf of Best for Britain, YouGov surveyed 13,433 people between 27th May – 11th June 2026.

The survey was conducted using an online interview of members of the YouGov Plc GB panel of 400,000+ individuals who have agreed to take part in surveys. An email was sent to panellists selected at random from the base sample according to the sample definition, inviting them to take part in the survey and providing a link to the survey. 

The samples were weighted to the profile of the sample definition to provide a representative reporting sample. The profile is normally derived from census data or, if not available from the census, from industry accepted data.  

For the question presented to respondents, YouGov carried out a MRP (multilevel regression and post-stratification) analysis. Results were projected across all constituencies in Great Britain, with each multilevel model run with 3000 iterations across seven monte-carlo Markov chains. 

The full MRP model process took information gleaned from estimating a multilevel model between question response and respondent and area background and characteristics, and projected these findings down to all 632 British 2024 Westminster Parliamentary constituencies. 

The MRP model was built and designed specifically for this project and question topic.