I was employed in the automotive supply industry for many years until I retired. Unfortunately, I also knew Longbridge in the days of Red Robbo. What was actually going on at the time is still unclear, but it was the beginning of the end for Longbridge. Matters did improve, but the simple and sad fact was they couldn't make any money. They weren't on their own, either: Ford Dagenham, Peugeot Coventry, Rootes Group, and others.
The worst car factories I ever visited (in the 1970's) were in the USA - if you think UK factories were out-dated at the time, you should have seen some of theirs! I happened to see a programme recently about Dayton, Ohio, which was the 'home' of Caterpillar and GM Van production, now all moved either abroad or elsewhere in the USA. Dayton is something of a ghost town as a result. The other end of the spectrum is I also visited the new Honda, Toyota and Nissan factories in the UK, and they are right up there with the best in the world. Just a pity they're not British. It all comes down to hard-headed, hard-hearted economics.
G