If it's not on the credit card slip you signed, then I don't see that you're agreeing to it any more than you're agreeing to a EULA by opening a box. It's not a normal condition of sale. You could mention this to C&E.
I was wondering about this myself, and a bit of googling found your eljay post..
Boots now have signs up next to their Chip and PIN terminals saying something along the lines of "Further to notices posted around the store, by entering my PIN, I agree that 2.5% of the cost of my goods will be paid to BCS Ltd"