The only one I can think of is Phil Morton in Macclesfield. I haven't used him myself but phoned last summer regarding a problem that I had with my overlocker (Brother circa 1989). He said he would be able to service it and fit new cutting blades which I had sourced. As it happens I changed them myself (I'd done it previously about 6 years ago) and did a thorough clean at the same time, so didn't take the machine in.
What machine do you have? Janome's UK head office is in Stockport and they do servicing. I've had repairs done by them in the past. Brother also have a place in Oldham I think.