We can loosely test the OBR’s average of forecasts against how the UK compared to other countries since the
referendum. If we compare the UK to France and Germany, or take the average of the G7, there appears to
be no effect of Brexit on GDP whatsoever, because those countries, Italy and Japan also suffered from weak
growth after 2016. But using a synthetic control method – also known as the ‘doppelgänger method’ – to identify
which countries had the most similar growth path to the UK before 2016, and then measuring the difference in
growth between the UK and these countries afterwards, a gap of 5 per cent had emerged by the middle of 2022.