From the latest report from the Office for Budget Responsibility:
"But the strength of the rebound in demand in the UK and internationally has led it to bump up against supply constraints in several markets. In the UK, these supply bottlenecks have been exacerbated by changes in the migration and trading regimes following Brexit".
https://obr.uk/overview-of-the-october-2021-economic-and-fiscal-outlook/
Perhaps more importantly, from the OBR last May:
"The new trading relationship will reduce long-run productivity by 4 per cent relative to remaining in the EU"
"Both exports and imports will be around 15 per cent lower in the long run than if the UK had remained in the EU".
"New trade deals with non-EU countries will not have a material impact. This is because most of these largely replicate deals that the UK already had as a member of the EU and, in any case, they are likely to have only a very small and gradual impact on GDP".
https://obr.uk/forecasts-in-depth/the-economy-forecast/brexit-analysis/