what simcards are compatable in the uk

im new to arduino and would appreciate the help
im going to use the gsm module within my project and was wondering if all sim cards within the uk are compatable with it or if you need to go with a particular network?
im asking because virgin have a month on month contract that is very good for £11 per month but i dont want to commit if it wont work

any help would be greatly appreciated
many thanks

you could try: http://uk.truphone.com/

i am using the sim in the u.s., but tru seem to be based in uk.