Well, the 'bible' for UK ATC is the CAP493 (it is online at the CAA's website, type CAP493 is the search box, or even Google it).
Also, I'd imagine that whoever you're doing your training with will have some pointers of any study you can do beforehand.
The danger is getting too deep into the very dry publications without any interpretation for lecturers/instructors, and causing more confusion than help.