update 2.. I've spoken to the insurers again this morning, advising them that it should be free this afternoon and I'd like it to go to Sytner.
They kicked up a bit of a fuss about it "not being an insurance approved garage" blah blah, but when I pointed out that their full name was "BMW Sytner", a large, multi-store, official dealer of BMW, they decided to stop arguing.
However, they're saying they that if I take it to BMW, it can take up to five days for them to come and inspect it, meaning nothing is likely to get done until at least Wednesday next week (however, if I get it towed to their approved garage, which is in a totally different county, they can look at it within 24 hours).
TBH, I'm not letting them take it anywhere but BMW, but my concern is that BMW is going to be more expensive than their tinpot garage - how does that fair when in comes to repairs?
If BMW give me a quote that's over the market value of the car, but their indy gives one lower, do I have the right to say "move it to your garage then" rather than get it written off?
(Before anyone says it, I have NO intention of ever selling my car, so I'm NOT worried so much about resale value - so the fact the BMW don't do the repair work isn't really an issue other than my own personal satisfaction, so please, don't just say "just write off and get another"

Winston's my baby!)