Yes. Gambling transactions are treated as cash withdrawals. All pound sterling cash withdrawals are subject to a withdrawal fee (2.5%, minimum £2.50). In addition, you'll pay interest on this cash from the date the transaction settles to your account.
If these transactions take you over your cash limit (30% of your credit limit or £500 per day) we may stop you making further transactions. You'll find all the information on how we treat cash in your agreement and on your monthly bill.