The academics said in the report that the Treasury’s forecasts were pessimistic about the prospect of future trade deals after Brexit: “Analysis by HM Treasury of the potential impact of various outcomes for trade outside the EU is examined and found wanting.
“Instead the actual experience of UK export performance is examined for a long period including both pre- and post- accession years. This suggests a more limited impact of EU membership.
“While we include a scenario based on Treasury assumptions, a more realistic, although in our view still pessimistic, scenario assumes half of the trade loss of the Treasury. The results are presented through comparing these scenarios with a pre-referendum forecast.”
Business investment would fall by between 7 per cent and 15 per cent from 2017 due to the uncertainty of Brexit, the report said.
However it said that these falls “are largely due to uncertainty and diminish from 2019 once the UK leaves the EU”.
A HM Treasury spokesman said: “We want the best outcome for Britain.
“That means pursuing a bespoke arrangement, which was not what the Treasury’s pre-referendum analysis was based on.
“This will give British companies the maximum freedom to trade and enables us to decide for ourselves how we control immigration.”