"The Darkroom Uk Ltd" Cheltenham do a very good mail order service and the quality of their E6 processing is first rate. I've not used them to process anything else, but before I sorted my own B&W stuff their B&W hand prints were very good as well.
I did try to post a link to their website but for some unknown reason the forum now says I have never made any posts before and as such can't include links until I've made 5 posts!!!! I know I don't post often, but I've definately posted before!!!
All I can suggest is you do a google search for "Darkroom UK Ltd"