I'm not far from you and found that locating a good repairer is a problem..... several I've used have attempted to stitch me up at times.... I had ones MOT licence removed because it was so blatant.
I bought a 638 traveliner a few months ago that had just had £800+ work done on the injectors.... black death, stripped and serviced the injectors and set it up........ done in birmingham a couple of weeks before I bought.
After a couple of days I was getting fumed out..... had exhaust, insulation... everything checked as it couldn't be the injectors as they had just been done (£800+ is way over the odds but I've got the receipt)............. I am arranging to drive it over to knaresborough (other end of the A59 from 'pool) at least I know they're good on mercs, reasonably priced and above all I trust them.
the job that was done in birmingham would have been £350 in knaresborough and I would bring it back in the day (a forced rest with my feet up in a local hostelry (getting dead posh ain't I))
probably too far for you but just in case its Stewart at indigodieselservices.co.uk and mention email@example.com
from the benzworld forum........ several members have used him with great success.