This company in Croydon did an excellent job on one of my previous cars:
http://www.fleetline.co.uk/index.asp
One of the chaps in the bodyshop did the work after hours charging me essentially cost for the parts, and a fairly reasonable hourly rate for his labour (cash in hand). If the work is not covered by insurance and you'll be paying it yourself, I'm sure they'll do you a deal.