Government's own analysis January 2018. 'The "no deal" scenario, which would see the UK revert to World Trade Organization (WTO) rules, would reduce growth by 8% over that period. The softest Brexit option of continued single-market access through membership of the European Economic Area would, in the longer term, still lower growth by 2%.' And in terms of all those trade deals, here are the projected numbers... 'The analysis assumes in all scenarios that a trade deal with the US will be concluded, and that it would benefit GDP by about 0.2% in the long term. Trade deals with other non-EU countries and blocs, such as China, India, Australia, the Gulf countries, and the nations of Southeast Asia would add, in total, a further 0.1% to 0.4% to GDP over the long term.'