There has been immediate criticism that thIs report is just another case of bad forecasting about Brexit outcomes. First look at the source of the report and then answer the question;
"Is this a case of cognitive bias by avid Brexiteers"?
That didn't happen by chance. As Robert Peston reported, the work was collated from various departments via the Government Economic Service and the analysis done by the economics team at DExEU. They've asked secretaries of state to bring their own departmental chief economist to any presentations if they want the assurance of them challenging the findings. Some of the standard Brexiter attacks have already been used against the leak - that no-one listens to experts anymore, that the future is impossible to predict, that Project Fear doesn't work, blah blah blah. ... this work is bullet-proof in terms of its sourcing. It has impeccable Brexit credentials. Unless we are going to give up on the idea of governments trying to work out what the impacts of their actions are, we will want reports like this.