If its a company car it will be company insurance so the whole thing will make no baring on his insurance or renewals whatso ever, its just grief he doesnt have to deal with.
I had a similar accident a couple of years ago (guy just slammed into the rear quarter of my lupo spinning it round then hit the front and pushed me onto the A1). Is his witness a passenger? if they are the insurance company take their side with a pinch of salt.I had to say it but roundabout accidents inevitably go 50/50, both my insurance company and his said that to me at the first contact with them. There would have been cctv covering my accident as well proving what happened. But roundabouts they just do it 50/50. Girl i work with had the same thing as well, and a friend of mine that works for a solicitors that deals with claims said the same thing.
I know its a real real pain in the arse as its not your fault, keep fighting it and i hope it gets you somewhere