I searched on froogle.co.uk for 6GB RAM and that's the kind of result I got. Same for 3x2GB RAM. xD Didn't check much beyond the lowest price for all results.

EDIT: The site I go to when mass-purchasing tends to be Overclockers UK, although I generally check Froogle to see if I can do better by keeping certain parts ordered elsewhere. Sometimes I can, but usually the shipping costs from multiple sites causes issues. I think things in the UK are just more expensive in general. =/