Question to the HM Treasury:

To ask the Chancellor of the Exchequer, what assessment has been made by her Department of the statistical reliability of the OBR's claim that the UK economy is growing more slowly than if the UK had remained in the EU after 2021; and if she will set out the analysis, facts and arguments behind the assessment.

The Office for Budget Responsibility (OBR) is the Government’s independent official forecaster and is responsible for producing economic and fiscal forecasts.

The OBR has included assessments of the economic impacts of leaving the EU in its forecasts since 2016. In March 2020 the OBR estimated that GDP will be 4% lower in the long run than it would have been had the UK not withdrawn from the EU. As of the Spring Forecast 2026, the OBR’s assumptions were unchanged from its previous assessment.

The OBR is required to produce a Forecast Evaluation Report (FER) each year under the Budget Responsibility and National Audit Act (2011). The OBR is required to explain the reasons for divergence between its forecasts and subsequent outturns, to support future forecast improvements. The OBR’s latest FER was published in June 2026 and can be found on its website.