UK productivity is 4% lower than it would have been had the United Kingdom remained in the European Union.

Omissions

• The 4 per cent productivity figure and the 15 per cent trade figure are the OBR's long-run modelling assumptions (an average of external studies), not measured outcomes of the post-Brexit period to date; the OBR explicitly says the reduction 'builds over time' until the full effect is reached.
• By the OBR's own estimates only about one third of the long-run productivity impact had been realised so far, so presenting '4 per cent' as the current level of lost productivity overstates the effect already observed.
• The 15 per cent refers to the volume of imports and exports / overall trade intensity in the long term, and the OBR's Brexit trade assumptions are contested by other economists (e.g. the Institute of Economic Affairs), so the figure is a modelling assumption rather than a settled empirical fact.
• Some OBR material underlying these numbers was published before the session (e.g. the April 2023 Brexit analysis), i.e. the figures are several years old and were framed as projections.

Sources

• PrimaryOffice for Budget Responsibility (OBR) — 'How are our Brexit forecasting assumptions performing?'"On trade and productivity, we assume that the volume of UK imports and exports will both be 15 per cent lower in the long run than if we had remained in the EU... And we assume that this leads to a 4 per cent reduction in the potential productivity of the UK economy. The reduction builds over time with the full effect..."
• PrimaryOffice for Budget Responsibility (OBR) — 'The effect on productivity of leaving the EU'"With the impact of Brexit on productivity already having reached 1.4 percentage points, according to our estimates, around one third of the long-run impact is..."
• PrimaryOffice for Budget Responsibility (OBR) — Economic and fiscal outlook, November 2025"...Brexit, which we continue to expect to reduce the overall trade intensity of the UK economy by 15 per cent in the long term."
• SecondaryInstitute of Economic Affairs — 'Has Brexit Really Harmed UK Trade? Countering the Office for Budgetary Responsibility's claims'"The OBR's April 2023 Brexit analysis claims that Brexit will reduce long-run productivity by 4 per cent relative to remaining in the EU..."
• SecondaryGreater London Authority — 'Overview of recent studies on Brexit's economic impacts'"The Office for Budget Responsibility's (OBR) analysis of Brexit impacts suggested that 'the volume of UK imports and exports will both be 15 per cent lower...'"