Was in Boots at The Fort, Birmingham, and spotted boxes of shaver replacement foils and cutters at knock-down prices. Generally have stickers saying £3 for foils and £5 for cutters. Got to the checkout and they came up at half that price!
Mostly Remington (to fit models beginning TA or TF), some others as well.
May be specific to this store but worth checking if you're in a Boots.