is it mastercard or visa?
MasterCard will only work at some sportbooks, not at any MG online casino directly. VISA should work at all casinos for UK cardholders, but beware the T & C of the individual card company, as the cumulative fees could differ widely.
Debit cards will probably be the best option as provided you play in the same currency as the account behind the card, there will be no fee. I have had my Lloyds debit card declined at casinos, but my Cahoot debit card works fine, and winnings can be sent back through it for some casinos. Cahoot also pay interest on the current account behind the card, unlike Lloyds. I would assume that a Barclays debit card will work, as they have the most lax attitude towards gambling transactions on their credit card.
My First Direct VISA credit card also seems to charge no fees for gambling transactions, even though the T & C say I should be charged interest as for cash advances from the date of transaction.
Barclaycard also count winnings withdrawn back to the card as payments towards your statement balance, and going heavily into credit from a big win does not seem to bugger up the system (I have done this a few times
).
This may not last, card companies are tightening up their criteria, and many would like to discourage gambling transactions without going so far as to ban them altogether.
Another problem I have recently found is that casinos will ONLY pay winnings back to the card, and not Neteller, which has left me with an empty Neteller account and a "full" Barclaycard - which means I have to deposit and withdraw through the card unless I withdraw from a casino that does not currently pay back to UK VISA cards. It does have the benefit of making it harder to gamble, as there are strict limits on the amount that can be deposited by cards, but no such limits on what I can deposit through Neteller.
Moving my winnings from the card to Neteller costs 9%, and is not going to happen unless the casino makes it worth my while with a very juicy bonus.