As other comments have noted, the point is that the EU will not want to give the UK a good deal on leaving, because the EU does not want to give any encouragement to the other countries which want to leave the EU (some of which want to leave more strongly than the UK do - apparently). Secondly, why would the UK end up with a Norway or Switzerland deal, when the UK is the 5th largest economy in the world? This is unpr…
So what you are saying is that brits will stop buying German/EU cars? Where are they going to buy their cars from? It's not like UK has some meaningfull car making industry, they moved all factories away. Not everyone can buy an Aston Martin.
I think that as long as the price for an EU car will be just below the price for importing an equivalent car from US or Asia, brits will have no other choice but to buy from Germans, even with new taxes added.