I've used both a debit and a credit card with them with no problems. Last year I phoned to get a rate over the phone, which was better than the online offer at the time so be sure to ask for the special rates. They only take the card number as security. You settle the bill when you check out and dont have to pay with the card you used to make the booking. The only exception is if you do an advance purchase special price where you pay upfront for a good rate that is not refundable and cannot be changed.