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New research from Best for Britain, based on a megapoll by YouGov, suggests that committing to EU membership could be the difference between a Labour-led and Reform-led government at the next election. A commitment to EU membership could bring the Labour Party to 321 seats, just five short of a majority in the House of Commons, the study found.
Best for Britain commissioned YouGov to carry out a survey of 13,433 people between May 27th – June 11th, 2026. The poll tested how respondents might vote based on different hypothetical Labour Party policies on the EU. YouGov then carried out MRP (Multilevel Regression and Post-stratification) analysis to estimate the vote shares of each Westminster Party in the 632 constituencies in Great Britain (excluding Northern Ireland). Best for Britain layered additional analysis on top of the YouGov MRP to reflect the practicalities of a General Election.
The poll asked respondents which party they would vote for if a general election were held tomorrow. They were then asked how they would vote if the Labour party adopted the following positions:
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- Pursuing closer relations without joining the Single Market, a Customs Union, or the EU itself (the current government position, based on red lines in the 2024 manifesto)
- Joining a Customs Union
- Rejoining the Single Market
- Pursuing full EU membership
How could Labour’s vote share be improved by pursuing EU membership?
YouGov’s MRP showed that if Labour committed to EU membership then its national vote share could increase to 37%, against a baseline in June of 18%; a marked improvement from its current standing. While pursuing a closer relationship with the EU brings its vote share up, relative to the baseline, full EU membership added an additional 11%.
The consolidation of the progressive vote behind Labour, from both Lib Dem and Green voters, as well as the policy’s potential to persuade undecided or disengaged voters, could allow Labour to outperform Reform UK considerably and stop Farage from entering No10.
Who would be most likely to win the next election if Labour stuck to its policy of pursuing closer relations?
If Labour was to stick with its current EU red lines and only pursue closer EU relations, then Best for Britain’s analysis suggests the party would be unlikely to form the next government, and that Nigel Farage’s Reform UK would emerge as the largest party in Westminster. In such an event, Reform UK was projected to win 300 seats compared to Labour’s 136.
Who would be most likely to win the next election if Labour pursued a Customs Union?
If Labour was to pursue a UK-EU Customs Union, they would be likely to form a coalition government alongside the Liberal Democrats. In such a situation, Labour was projected to win 256 seats, which – alongside the 72 seats estimated for Ed Davey’s party – would deliver a slim majority of two seats. In this scenario, Reform UK was modelled to win 235 seats as the second largest party.
Who would be most likely to win the next election if Labour pursued joining the Single Market?
Pursuing joining the Single Market would also likely create a scenario for Labour to form a coalition government alongside the Liberal Democrats. In such a situation, Labour was projected to win 257 seats – just one more than when pursuing joining a Customs Union – and the Liberal Democrats were forecast to win 72 seats. In this scenario, Reform UK was modelled to win 230 seats as the second largest party.
Who would be most likely to win the next election if Labour pursued EU membership?
If Labour was to pursue full EU membership, Labour would likely be within touching distance of a parliamentary majority. In such a situation, Labour was projected to win 321 seats, compared to just 191 for Reform UK. This scenario estimated that the Liberal Democrats continued to win 72 seats.