whatwouldrondo
Actually, despite the inefficiencies we see in our daily life, many parts of the world are even harder to do business.
UK has been the 4/5/6 largest economy since WW2 before and after Mrs Thatcher. Even in the dark days of the 70s, she was still more efficient that many parts of the world (such as Mao's China ).
Our economy is broken down as 72% domestic and 28% export (goods+services). 44% of the 28% = 12.3% (of the GDP) of the is EU dependent.
Out of the 12.3%, some of those can be consumed locally in replacement of other EU imports, some will find other markets, some are not price sensitive enough etc. I would say even if we trade under WTO rules, what is 'at risk' is probably about 5% of the GDP - a very large number, but not life and death.
Now, we need to look at what barrier EU-WTO tariffs imposes. For manufactured goods, it is less than 10% (and many 2-4%). Currency depreciation and a little bit of state aid should sort that out if necessary.
Fisheries, Agriculture and textiles face very high barrier - those will suffer.
Financial services will be somewhat affected and will need to route their activities through EU subsidiaries and remit their profits via dividends back to the UK shareholders. Many bigger institutions such as Goldman, HSBC etc already have multiple license, so it is a matter of internal restructuring of their activities.
Educational services - we will just sell more to full fees paying international students (not EU rate). The research funding side needs to be replaced and more collaboration with the US will occur. The Belgium Professor (Peter Piot) who discovered Ebola said if UK was not in the EU, he would have further his career in the US - note - not France, Germany or elsewhere - so our competitor is the US.
Free from EU state aid restriction, we will be free to strategically 'help' our industries during the transition period.