Google Pay lets you pay in apps and on websites by choosing "Buy with Google Pay" and confirming with your phone's unlock method. As HSBC explains, a virtual account number represents your card, so the merchant does not see your real card number and your card details are not stored on the phone itself.
Like Apple Pay, Google Pay can hold both debit and credit cards. Licensed British casinos cannot accept credit card payments for gambling, so make sure a debit card is selected before you deposit. You can pick a different card for a particular app, and it then becomes the main card for payments there.
Not every casino pays withdrawals back through Google Pay, so check the cashier page for the withdrawal method that applies and the operator's stated processing times.
Google Pay is a convenience layer, not a separate account, so the UK rules on the card underneath still apply in full.
Source: www.hsbc.co.uk