I'm sorry for the UK but they voted for Brexit. Can't take the bad with the good, whatever that might be in their eyes. I don't see why they should receive special treatment.
This is the European Automobile Manufacturers association trying to stop costs of billions from importing cars and parts to the U.K. (and technically vice versa). It’s the likes of BMW and Peugeot that it will hurt.
It probably costs less than 10% of MSRP to transport a car (or the parts) via cargo vessel from China or the US, so prices in the UK will go up less than 10%, and EU's EV automotive factories will need to cut production targets (at the same time as the EU is subsidizing them in order to increase production).
There are a few UK based companies (Aston Martin, Bentley, Lotus, ...) that are probably too small to route around the tariff, but they're all high-margin, and their customers aren't particularly price sensitive.
https://en.wikipedia.org/wiki/List_of_car_manufacturers_of_t...
This is complicated by the fact that the whole process of re-joining would likely take longer than a single term to complete, and the EU is unlikely to start that process until they believe that support for it in the UK is strong enough that the whole thing won't just be abandoned part way through due to a change of policy or party in government.