Hi there
I only have heard of a few places, & I have no affiliation with any of these companies.
1. Dent Devils they are a franchise and are national.
2.Sleek Lines ( independent) Lightwater area of Junction 3 on the M3.
3. Harvi ( independent) Welling Kent and apparently does mobile work also 0790 9682 343.
Hopefully it is of some use to you..?