I would have said fusion Motorsport, but it seems they are now not accepting any general work as only doing full blown Motorsport.
Norris designs have had their hand in a long time now as a company, so should have good knowledge.
Interpro automotive in Thornbury Bristol have always been very helpful and only ever heard good things about them (you will need to book in advance as usually busy).
There used to be a place in nailsea, Protech, not sure if they are still around, but I had a couple of bad experiences with them and I personally wouldn't go to them (20 years ago though lol)