I’ve had a few bits serviced by Mike Powell in Bolton. Everything was good and I have no hesitation in recommending him:
http://www.mpavservice.co.uk/
He is one of a dying breed so he does have a bit of a backlog at times, but he knows his stuff. And when you visit his workshop, the examples of classic HiFi esoterica waiting its turn to be rejuvenated is quite eye opening!