Practically every online bingo site in the UK will ask you for card details when you sign up, even if you don't intend to make a deposit. Using a card can be a quick way for the operator to ensure your name and address is verifiable and in most cases you are over the age of 18. Even if you are required to sign up and enter your card details, absolutely no money will be taken from your card without you expressly choosing to make a deposit at the bingo site.