Recent estimates put the UK economy about 4–8 % smaller than it would have been inside the EU; trade and investment took the heaviest hits.
Britain is the only member state ever to have left the EU, which makes Brexit the closest thing Europe has to a natural experiment. Ten years after the referendum, there is enough data to judge it.
The size of the hit
Nobody can observe the Britain that stayed, so every estimate builds one.
- The Office for Budget Responsibility, the UK’s official fiscal watchdog, assumes the trade deal with the EU will leave productivity 4 % lower in the long run and exports and imports both about 15 % lower. It still uses that assumption in its 2026 forecasts and estimates that about two-fifths of the productivity hit had already happened before the deal took effect, as uncertainty held back investment.
- A study published by the National Bureau of Economic Research, revised in June 2026, compares the UK with a synthetic control built from 33 similar economies and with a survey of British firms. It puts UK GDP 6–8 % lower by the end of 2025, investment 12–13 % lower and employment and productivity each 3–4 % lower.
- Goldman Sachs economists put the cost at about 6 % of GDP in a ten-year retrospective in June 2026, within a range of 4–8 % depending on the comparison group, as reported by the financial press.
- The National Institute of Economic and Social Research estimated 2–3 % of GDP by 2023, rising to 5–6 % by 2035.
None of these bodies finds that leaving has made the British economy larger. The largest figures draw the sharpest criticism: the economist Julian Jessop points out that the United States dominates the NBER’s synthetic Britain, and American growth has outpaced Europe’s, which would inflate the gap. That argues for a smaller loss, not a gain.
Trade: goods hit hardest, small firms first
The trade data show where the cost lands. Researchers at the London School of Economics found that the trade agreement with the EU cut UK goods exports by about £27 billion, or 6.4 %, in 2022, and exports to the EU by 13.2 %. About 16,400 firms, 14 % of those that had sold to the EU, stopped exporting there. The smallest exporters, with six or fewer employees, saw their EU sales fall by 30 %; large firms were barely affected. Customs declarations, certificates and rules of origin are a fixed cost, and a fixed cost hurts small firms most.
The Resolution Foundation reported in June 2026 that UK goods export volumes have fallen more than those of any other G7 country since 2019. Services now make up 59 % of UK exports. That share has risen mostly because goods fell, the authors note, and it gives no evidence that services were boosted by leaving.
Labor: fewer Europeans, many more arrivals from elsewhere
Free movement ended with the transition period at the start of 2021. Immigration did not fall. The Office for National Statistics estimates that net migration peaked at 944,000 in the year to March 2023, driven by arrivals from outside the EU. In the year to December 2025, provisional figures put net migration at 171,000: more EU citizens left than arrived (−42,000), non-EU net migration was +350,000, and 136,000 more British citizens emigrated than returned.
Trucking shows how hard it is to separate causes. In the year to June 2021 the ONS counted 268,000 heavy-goods drivers, 53,000 fewer than in 2017. EU drivers fell by 12,000, or 30 %; British drivers fell by 42,000, and much of the drop came during the pandemic.
Northern Ireland: the special arrangement
To avoid a land border on the island of Ireland, Northern Ireland stayed inside the EU’s rules for goods. The arrangement began as the Northern Ireland Protocol and was reworked in February 2023 as the Windsor Framework, which added a “Stormont brake”: 30 members of the Northern Ireland Assembly from at least two parties can ask London to block changes to the EU goods rules that apply there. In December 2024 the Assembly voted 48 to 36 to keep the arrangement, without the support of any unionist member. Because the vote was not cross-community, it must be repeated in 2028.
What the UK gained
Leaving brought real powers. The UK runs its own trade policy and used it: it joined the CPTPP, the Pacific trade pact, in December 2024, and signed a free trade agreement with Australia, among others. The OBR does not expect these deals to matter much; the government’s own estimate for the Australian agreement is about 0.1 % of GDP over 15 years. The UK sets its own migration rules, and it stopped paying into the EU budget.
Since 2024 the British government has moved back toward Brussels. At a summit in May 2025 the two sides signed a security and defense partnership and agreed to negotiate a food and animal-health agreement, a link between their carbon markets and a youth experience scheme. Talks on British participation in the EU’s SAFE defense loans failed in November 2025.
What the British think now
In a YouGov poll in June 2026, 57 % of Britons said voting to leave was wrong and 30 % that it was right; 61 % called Brexit more a failure than a success. In September 2026, 59 % told YouGov they would support rejoining and 32 % would oppose it. Support drops when the price is spelled out: if rejoining meant giving up the opt-outs Britain had as a member, such as staying out of the euro and Schengen, 35 % were in favor and 43 % against.
What the experiment shows
The legal route out works. The price is paid in trade, investment and the hours small businesses spend on customs forms. Britain paid it as a large economy with its own currency and a global financial center. A smaller country that sends most of its exports to the EU would have less room to absorb the same shock.