If I remember the figures quoted on the BBC correctly (and I haven't checked), 78% of cars made here are exported, and 86% of bought here are imported.
Of course, with the actual manufacture of the car itself being ony part of the picture, the other part being all the secondary jobs in parts suppliers. component manufacturers, and so on, it's a good deal more complicated than simple unit production of cars might imply.
However, I agree with you, in large part. Germany and France both have much more riding on car manufacture than we do, though it's still a big employer.
The critical question in all this is whether this proposed move is a sound treatment for the industry, or a short-term sticking plaster.
Right now, the industry has vast fields sitting full of unsold new cars. Bargains are already out there in dealerships for the asking for those with cash. But once those stocks have gone ...... ???
Our financial problems are NOT short-term. The car industry is going to have to accept that the economy has major problems, that banking has changed and cheap, easy credit is gone either for good or at least for a long time, that the "second income" effect of house price inflation has gone for even longer and that most people are looking to cut down on debt. All in all, there's been a seismic shift in consumer confidence and a degree of belt-tightening that means the car industry is going to have to live with changed times.
So while car manufacturers might want government help to shift those huge stockpiles, I'll bet that having done so, prices will rise, plants will get shut, workforces will get cut drastically and mercilessly and that commercial realities will drive that, regardless of what Government want .... or the political cost of unemployment.
This move IS, in my view, a sticking plaster, not a real treatment for our economic woes. It's designed to shift the cars the makers are stuck with, but even more, it's designed to shift the economic pain of that extra unemployment past the date of next election.