DVD3500: You're correct. With the proviso about the value limits, I too haven't got my head around that yet. It is made even more confusing as my wife buys lots of embroidery stuff from a firm in Scotland so far not a single centime in taxes, although the orders are quite small as a rule and mostly European manufacture, or at least not declared as other than that.
The cars would count as UK manufacture I'm sure. The rules relate to the percentage of the value originating in the UK. This works for goods from the UK to the EU. The other way round ? Good question one would assume the agreement is the same but I can't swear to it, I've had no need to look it up.