Just ordered some currency myself on the BA/TravelEx site. Before paying it says:
There are no card handling fees charged if you choose to pay by Debit Card or Visa Credit Card. If you wish to pay by MasterCard Credit Card, we will levy a handling fee of 1.5% of the order value (min £4.00 - max £15.00). This will be shown within your order summary. If you choose to pay by either MasterCard, Visa Credit Card or Visa Debit Card, your card issuer may apply a cash advance charge which will be shown separately on your Credit Card/Bank statement
.