I've seen Digitalab recommended on LandscapeGB for E6 processing. I think they do scanning too, but there were various other recommendations on the LandscapeGB for MF scanning, I think in a film comparison article. I've used Digitalab for developing colour negatives, and they were fine. Their prices look very competitive.
A lab I would offer caution about is one based in Burnley...my credit card details were fraudulently used in Colne (down the road from Burnley) the same day to buy GBP 20 of pet shop stuff...took me ages to convince my credit card company to reverse the charge.