UK GDP per capita was 6–8% lower by 2025 than it would have been had the UK remained in the European Union, according to analysis published in December 2025 by UK in a Changing Europe. The same body, writing in June 2026 as the ten-year post-referendum mark approaches, reaffirms that Brexit has made the UK economy structurally smaller than the counterfactual trajectory would have produced — a conclusion that, by now, sits closer to consensus than controversy among mainstream economists.

These numbers are not new in kind, but the accumulation of time matters. The longer the horizon over which the output gap persists, the harder it becomes to attribute it to transition noise or temporary adjustment costs. What UK in a Changing Europe calls a "large and persistent cost" is precisely that: persistent.

The Contours of the Output Gap

To make the 6–8% figure tangible: UK GDP per capita in 2025 ran at roughly £33,000–£35,000 depending on the deflator used. A 7% gap — the midpoint — translates to somewhere in the region of £2,300–£2,500 per person per year in foregone output. Compounded across a working population and a decade, this is not a rounding error. It is a structural drag that feeds through into tax revenues, public services, and wage growth in ways that are individually diffuse but collectively significant.

The mechanism is not mysterious. Leaving the EU single market introduced non-tariff barriers — rules-of-origin requirements, sanitary and phytosanitary checks, customs declarations — that raise friction and cost for goods trade in both directions. UK goods exports to the EU fell sharply in January 2021 following the end of the Brexit transition period, before recovering into February 2021, according to House of Commons Library research. That January dip was, in retrospect, a preview rather than the full story: the longer-term effect has been a persistent reduction in trade intensity that gravity models have consistently flagged as below the predicted level for an economy of the UK's size and proximity to European markets.

Services trade adds a further dimension. Financial services passporting ended. Professional qualifications face mutual recognition barriers. UK-based firms that previously supplied EU clients through a single regulatory framework now navigate 27 separate jurisdictions or have re-domiciled EU-facing operations to Dublin, Amsterdam, Frankfurt, or Paris. These costs are harder to count than goods data, but they are real.

What Government Projections Said — and Didn't

Against the empirical record, the UK Government's own modelling deserves a direct reading. The Office for Budget Responsibility's Brexit analysis — published in late 2021 — estimated that Brexit would raise UK GDP by 0.1% over 15 years, reflecting whatever trade deal gains the Government projected offset against the costs of leaving the single market and customs union. That 0.1% figure was itself widely regarded at the time as optimistic by independent economists, and it was already net-negative relative to remaining in the EU — just less negative than a no-deal scenario.

The divergence between a 0.1% long-run gain and a 6–8% per-capita loss relative to counterfactual is not a simple apples-to-apples comparison. Government projections modelled Brexit-in-isolation; the UK in a Changing Europe analysis uses synthetic control and similar counterfactual methods to estimate what the UK economy would have looked like under the alternative of continued membership. The methodologies differ. But the directional disagreement — a gain versus a loss — is stark, and the weight of post-hoc empirical work has, by 2026, largely settled on the loss side.

Public Perception Has Tracked the Data

Public sentiment, which rarely moves in lockstep with economic analysis, has in this case converged toward the empirical picture. As of 2023, two-thirds of UK respondents believed Brexit had damaged the economy, according to UK in a Changing Europe polling. More striking still: only one in five Leave voters assessed the impact as positive. That is a significant erosion of the political coalition that carried the 2016 referendum — not a reversal of political identity, necessarily, but a candid acknowledgment of economic cost even among the vote's supporters.

Public perception is not economic data, and it should not be treated as such. But in a democracy where political economy shapes policy choices, the collapse of confidence in Brexit's economic case among a substantial fraction of its own proponents is a relevant data point for anyone modelling future policy trajectories, including trade negotiations and the question of whether regulatory alignment with the EU will deepen or hold steady.

Historical Pattern

Those of us who covered the early years of the commercial internet will remember a structurally similar dynamic: the costs of a major transition were felt immediately and concretely, while the promised benefits were deferred and diffuse. The dot-com bust was real; so was the decade of productivity and commerce that followed once infrastructure and business models matured. The important difference here is that internet adoption was a one-way technological ratchet — once consumers and firms had broadband, there was no going back. Trade barriers, by contrast, are a policy variable. They can be raised and, in principle, lowered again. That distinction shapes the time horizon over which the UK's economic relationship with Europe will continue to evolve.

What Comes Next

The ten-year horizon is a natural prompt for reassessment. The UK–EU Trade and Cooperation Agreement left significant scope for future negotiation: financial services equivalence, Mutual Recognition Agreements on conformity assessment, and the possibility of deeper regulatory alignment in specific sectors are all on the table in varying degrees. A reset on veterinary and SPS checks — already the subject of exploratory talks as of mid-2026 — would directly address some of the goods-trade friction that drove the January 2021 export collapse.

None of this erases the accumulated output gap. An economy that has run 6–8% below trend for roughly four years does not catch up simply because the underlying policy friction is reduced. The foregone investment, the relocated operations, the talent that moved or did not move — these have real hysteresis effects. But the gap between the current trajectory and an improved one is narrower than the gap between current and counterfactual-membership, and in policy terms, the former is what governments can actually close.

Looking at what this means for firms and practitioners: the persistent trade friction is now the operating baseline, not a transitional anomaly. Supply chain architecture, regulatory compliance frameworks, and market access strategies built around EU–UK divergence are the appropriate planning assumption for the foreseeable future, even if selective re-alignment occurs at the margins. Any material change to that baseline will be signalled well in advance through the formal TCA review mechanisms — the next scheduled comprehensive review falls in 2026 — giving businesses adequate lead time to adjust.

The economic cost of Brexit is now sufficiently documented, and sufficiently durable, to be treated as a structural feature of the UK economic landscape rather than a contested hypothesis. The policy question — what to do about it — remains open, and genuinely contested on grounds that go well beyond economics. That argument is for another column.