As you are in the UK, how far are you from a Poundland shop? They sell Agfaphoto Vista Plus 200 for, you guess it, a 1.
For development I recommend Snaps Photo services: http://www.snapsphotoservices.com/
For buying films other than Agfaphoto, google Ag Photographic, Silverprint, RK Photographic, Mathers of Lancashire, Discount films Direct, Mailshots, Morco, Firstcall Photographic.