Question to the HM Treasury:

To ask His Majesty's Government, further to the reply by Lord Livermore on 13 October (HL Deb col 9), on what basis and calculations it was claimed that "without Brexit, GDP would be 4% higher".

The statement was based on independent analysis by the Office for Budget Responsibility. In 2020 the OBR forecast that GDP will be 4 per cent lower than it would have been had the UK not withdrawn from the EU. The OBR estimated that around two-fifths of the 4 per cent impact had already occurred by the time the EU-UK Trade and Cooperation Agreement came into force, that GDP would be 2.7 per cent lower by 2025, with the remaining reduction occurring by 2031.

In the OBR’s March 2024 Economic and Fiscal Outlook, they reaffirmed these assumptions were on track, and as of Spring 2025 these forecasts were unchanged.

Other independent studies are also consistent with this analysis, for example the National Institute of Economic and Social Research estimates that GDP will be 5 to 6 per cent lower as a result of Brexit.