I like this question on their money grabbing website...
Q. I have Credit and Debit cards. Which should I use?
A.We will gratefully accept donations from both Credit and Debit cards, although if the donation is greater than £15, we will be charged more for a Credit card donation than a Debit card donation.
So be a good JW and use your debit card for larger donations........it'll save the asshats money :)