ps. This is one time the great and good at Which have it wrong:
"While the cost to companies for processing a payment by debit card is around 20p, and no more than 2% of the transaction value for a credit card, Which? researchers found dozens of examples of companies charging far higher fees."
Let me assure you, the Paypal figures quoted above are far more typical of any small business.
Perhaps the figures from Which are more appropriate for M&S and Easyjet.