Just get on Autotrader and print out loads of adverts for very similar cars (nationwide). That'll give you an idea of value and if the insurance company come back with a lower offer then you can provide them as evidence that you can't replace the car like for like for less that £x
As said above, find 10 with the same mileage/age/spec. and print the prices out, then when they come back with bottom book you can send them copies of the ads. Only way on an 8 year old car, specially one that sells for way over book.
Wow, sorry to hear its been nicked. Do you mind if I asked what happened?
I've always considered my 530 Sport to be the ultimate in un-nickable cars - far too much hassle to break into and steal, so you need the keys, yet not worth enough to be worth the hassle of a home invasion.
Got £5k for a 2002 manual 530d SE with 86k with cloth seats a couple of months ago. I'd imagine at least £6k for a Sport, as the SE's are pretty undesireable.