After leaving, the UK will be in a weak negotiating position. Recession is almost certain, and even using an existing trade deal like CETA as a basis will take multiple years to negotiate because of the current UK red lines, like controlling their own immigration policy.

Canada had to adjust their immigration policy for several EU countries to get CETA. The UK will be over a barrel and will have to make major concessions.

Whether you're pro EU or not this situation is a total balls-up.