Personally, I'd get 2-3 quotes from a couple of decent coachworks first. Tell them it wont be an insurance job and you are likely to get even better prices. If your paying a £250 excess then your gonna have to fork that out anyway.
So , IMHO it might be better not telling the insurance for now, cut your loses and pay a cash repair and save on stupid insurance hikes in the long run.
Gus