What is a good digital photo print service for black & white in the UK?

I have some digital images, which on my screen look great in black and white (portraits). I’d like to have them printed, but I fear the dozens of print services out there: from what I read, they automatically ‘improve’ (retouch) pictures, which of course is mostly meant for simple colour snap shots; I’m happy with the current state of my pictures (provided my screen is well calibrated). The whole print process is likely focused on colour instead of black & white. Does anyone know a good company for black & white prints? Doesn’t have to be very cheap or so (although I’ll likely skip overly expensive).