As for car exports, it's obviously more complex: https://www.acea.be/statistics/artic...in-eu-partners
TL;DR the uk is a small country, and thus more reliant on external trade than a large trading block, like the EU, that has a larger internal market.
The uk was buying 12% of the EU's production quantity (and the EU is also exporting to other markets - 26%), whereas the uk's substantially smaller production was largely for export (81%) - primarily to the EU. And similarly for the suppliers. In terms of value the numbers were generally a bit smaller, as expensive cars are transported further.
And at least 10% of the automotive workers in the uk were from the EU.