Brexit reduced UK economic output by approximately 6% over the decade since the 2016 referendum, according to economists who analysed internal Bank of England company data. The same study, which used five additional conventional modelling methods alongside the corporate dataset, points to an average hit of around 8% when those wider approaches are considered together.

The data at the centre of the research is the Bank of England's Decision Maker Panel, a survey of British companies established in 2016 that was designed from the outset to capture the economic effects of Brexit. The Bank often uses the panel to assist in determining interest rates. Researchers tracked firms' self-reported exposure to Brexit, their accounts of its direct effects on their operations, and changes in their financial results over time. From this, they attempted to reconstruct how the UK economy would have performed had the referendum result gone the other way. Co-author Nick Bloom, a British economist at Stanford University, said the UK was growing at a strong pace before the vote and could plausibly have maintained at least some of that trajectory without the disruption that followed. He described the corporate data as providing meaningful corroboration for the study's broader conclusions.

The research identifies two roughly equal sources of economic damage. The first was the uncertainty that followed the referendum result itself. The period of prolonged political instability and unresolved negotiations weighed on business investment and decision-making well before any new trading arrangements came into force. The second came later, when the UK formally left the customs union and single market in 2021, introducing trade barriers that had not existed before. The study's conclusion is that these two effects together account for the output losses identified across the ten-year period.

Senior Bank of England officials have grown more direct in their public assessments of Brexit's economic consequences. Governor Andrew Bailey said recently that activity and growth had been lower as a result of leaving the EU, attributing this partly to the reduction in accessible export markets. He also pointed to effects on productivity and the overall scale of the market. His comments on financial services were more measured. While acknowledging the impact had not been positive, Bailey said it had fallen well short of the more severe outcomes that were widely predicted at the time of the vote.

The study has not gone without challenge. Some economists argue that constructing a credible counterfactual for UK growth is inherently difficult, given the number of major economic disruptions that occurred in the same period. Critics of the methodology point to the exceptional performance of US investment and technology industries, which inflated growth figures in comparable economies, and to the energy crisis that hit much of Europe from 2021 onwards. Those sceptical of the findings contend that studies of this type tend to attribute too much of the UK's relative underperformance to Brexit when other global factors were simultaneously pulling economies in different directions.

The paper is published just ahead of the tenth anniversary of the referendum. Its release coincides with a period of renewed diplomatic activity between the UK and the EU. Prime Minister Keir Starmer is due to meet EU counterparts at a summit in July, where agreements are expected to be reached on food and agricultural exports, electricity interconnection, and emissions trading. Further areas of alignment are also anticipated. Whether those talks produce substantive changes to the trading relationship that the study identifies as a source of lasting economic damage remains to be seen.