Try Kendall Car Repairs in Watford 01923-238058. Ask for Steve I used to know him well. He'll remember me (Dave Brettell) from my Escort Cosworths & Clio Williams. He did some plastic bodywork repairs on the side skirts on one of my cossies, and it was absolutely fabulous, and you couldn't tell it was ever there, plus he was cheap as.
I'm not sure if he still does bodywork, as I don't live round there anymore, but if he doesn't then there are 2-3 other repairers in the same lot, and I'm sure he'll sort you out with one of them instead at a good rate.
Let us know how you get on!
Cheers,
Dave