“Critics say my estimate – that the British economy is around 5 per cent smaller due to Brexit – is implausibly large. This insight tests their scepticism against other ways to estimate the cost of Brexit.

“In a debate I participated in last month, panellists were asked to say how much Brexit had curbed Britain’s economic output. Graham Gudgin of Policy Exchange and Cambridge University’s Centre for Business Research said he thought the costs had been negligible. Julian Jessop of the Institute of Economic Affairs said GDP was around 1 per cent smaller than it would have been, adding that the short-term impact was always going be negative, before the benefits of bespoke regulation and reduced trade barriers with the rest of the world kicked in.”