The trouble is, it's not as simple as "Once we're out of the EU, we can find new markets." UK industry is deeply enmeshed in the EU. A Guardian article (www.theguardian.com/business/2017/mar/03/brexit-uk-car-industry-mini-britain-eu) a couple of months ago took the example of a Mini produced in Britain.
I know not everyone will click on the link, so here's an excerpt:
If there is just one anecdote that succinctly sums up the problems that Brexit and the threat of tariffs pose to the UK car industry, it is this: the story behind the crankshaft used in the BMW Mini, which crosses the Channel three times in a 2,000-mile journey before the finished car rolls off the production line.
A cast of the raw crankshaft – the part of the car that translates the movement of the pistons into the rotational motion required to move the vehicle – is made by a supplier based in France.
From there it is shipped to BMW’s Hams Hall plant in Warwickshire, where it is drilled and milled into shape. When that job is complete, each crankshaft is then sent back across the Channel to Munich, where it inserted into the engine.
From Munich, it is back to the Mini plant in Oxford, where the engine is then “married” with the car.
If the car is to be sold on the continent then the crankshaft, inside the finished motor, will cross the Channel for a fourth time.