I think film is expensive from all high street shops that you're likely to encounter here as a tourist. Film is a little cheaper from specialist outlets such as Silverprint (www.silverprint.co.uk) and Mr Cad (www.mrcad.co.uk) but they're located in out-of-the-way places. I'd probably bring all my film in from the US if I were you. Over here, I always shop mail order to save $$$.