By Jennifer Hill

LONDON (Reuters) - Online gamblers could risk losing more than their stake if they use a credit card to fund their flutters.

Most credit card providers now treat online gambling transactions as cash advances -- which usually attract a higher rate of interest than purchases, according to price comparison site Moneynet.co.uk.

And while most cards offer up to 56 days' interest free on purchases, there is no such leeway on gambling transactions, meaning that punters incur interest from day one.

"Unless gamblers are aware that these transactions are treated differently from normal everyday purchases, they will be losing money hand over fist as the top rate of interest stacks up," said Richard Brown, chief executive of Moneynet.co.uk.

NatWest charges an interest rate of 12.9 percent on purchases on its classic credit card -- but that soars to almost double, 24.94 percent, on cash withdrawals.

First Direct charges 17.9 percent on purchases and 21.9 percent on cash.

Nationwide not only charges more interest on cash as opposed to purchases on its gold credit card -- 22.9 percent against 15.9 percent -- it also levies its cash withdrawal handling charge (the higher of 2.5 percent of the sum or 3 pounds) on online gambling transactions.

The Co-op charges a flat interest rate of 11.9 percent but hits online gamblers with its cash withdrawal charge, which is the same as the Nationwide's.