Politics & media · Brexit: what changed

Brexit and the economy

One number dominates this argument, and almost nobody quoting it means what it says.

View shareable visual summariesBrexit sectionWhat has been measuredWhat cannot be settled

The counterfactual warning

Counterfactual

Read this before the numbers

The 4% figure is a comparison with a Britain that stayed in the EU. That Britain does not exist, was never observed, and cannot be checked against reality. It is the output of a model, published by the government’s own independent forecaster, and reviewed twice since.

What it does not mean

  • It does not mean GDP is 4% lower than it was in 2016. GDP is higher than it was in 2016.
  • It does not mean every sector, region or household is 4% worse off. Some are better off and some are much worse off.
  • It does not mean 4% has already happened. The OBR judges about two-fifths of it had occurred before the trade deal even took effect, through investment uncertainty.

What it does mean

That the government’s independent forecaster expects the UK economy’s productive capacity to settle around 4% below where it would otherwise have been, and builds that into every fiscal forecast the Chancellor works to.

And it cuts both ways. A counterfactual cuts both ways. It is equally wrong to say “GDP grew, so Brexit cost nothing” — growth in the actual world tells you nothing about growth in the world that did not happen. Neither side gets to point at observed data and claim it settles a counterfactual question.

What the OBR actually assumes

The Office for Budget Responsibility is the government’s own independent fiscal watchdog. These assumptions are built into every forecast the Chancellor works to, which is why they matter more than any individual study.

15% lower Counterfactual
“Both exports and imports will be around 15 per cent lower in the long run than if the UK had remained in the EU.”
4% lower Counterfactual
“The post-Brexit trading relationship will reduce long-run productivity by 4 per cent relative to remaining in the EU.”
40% of the effect Counterfactual
“Around two-fifths of the 4 per cent impact had already occurred by the time the TCA came into force, as a result of uncertainty weighing on investment and capital deepening.”

The OBR has checked its own working. The OBR reviewed the assumption in March 2022 and again in March 2024, concluding on each occasion that it appeared broadly on track and that there was little in the data to suggest 15% was no longer a central estimate.

Office for Budget Responsibility, Brexit analysis ↗ — last updated 20 July 2026. Classification: Forecast / scenario — an assumption in an official forecast, not a measurement.

The part of the estimate that had already happened before the trade deal existed

This is the most useful and least quoted line in the OBR’s analysis. About two-fifths of the assumed 4% effect is judged to have occurred before the Trade and Cooperation Agreement came into force — through uncertainty weighing on business investment during the four and a half years between the referendum and the new relationship taking effect.

That reframes the argument in a way neither side finds comfortable. A substantial share of the cost is attributed not to the trading relationship that was eventually agreed, but to the period of not knowing what it would be. Whatever one thinks of the destination, the length of the journey had a price.

What has actually been measured

Everything above is modelled. Everything below is observed — which does not make it attributable to Brexit, only real.

The comparison that stops the simple story

−14%

Goods exports to the EU

vs 2019, real terms

−8%

Goods exports to non-EU

vs 2019, real terms. The control.

+28%

Services exports to the EU

vs 2019, real terms

+26%

Services exports to non-EU

vs 2019, real terms

Read all four, not one. Goods exports fell to everywhere and services exports grew to everywhere. The EU gap is 6 points on goods and 2 points on services. That pattern is consistent with a Brexit effect concentrated in goods, sitting on top of a global shift in the UK economy from goods towards services — and it is not consistent with either “Brexit destroyed our trade” or “Brexit made no difference”.

House of Commons Library, Statistics on UK trade with the EU (CBP-7851) ↗

What the data cannot settle

  • How much of the goods-trade weakness is Brexit?

    Unknown with precision. The pandemic, the energy price shock, the war in Ukraine and global supply-chain disruption all fall inside the same window, and non-EU exports fell too. Studies attribute a substantial share to Brexit; none can isolate it cleanly.

  • Would investment have been stronger inside the EU?

    The OBR judges yes, and attributes two-fifths of its productivity estimate to pre-TCA investment uncertainty. That remains a modelled judgement about an unobserved path.

  • Has any of it been offset by new trade agreements?

    Only marginally on the official assessments. The government’s own impact assessments for the Australia and New Zealand agreements projected GDP effects in the region of 0.1% or less over 15 years — real, and roughly two orders of magnitude smaller than the assumed EU effect.

Summary

The strongest official economic evidence points one way: the UK’s independent fiscal watchdog assumes a persistent aggregate cost relative to remaining, and has reviewed that assumption twice without changing it. The strongest observed evidence is messier: goods trade weak but weak to everywhere, services trade strong, investment recovered. Both of those sentences are true, and an account that reports only one of them is not describing the evidence.

Next: trade in detail, including the structural break in the data, and where Britain gained autonomy.