Hundreds of British gamblers stand to lose tens of thousands of pounds after a crackdown on online gambling firms with links to Britain by the US authorities, a leading gambling expert warned. The US Justice Department froze gambling accounts linked to three of the biggest online poker sites after accusing those running them of money laundering and fraud.

Prosecutors claimed the operators of Pokerstars, Full Tilt Poker and Absolute Poker – three of the most popular online poker sites – tricked US banks into processing billions of dollars from customers. US banks are prohibited from accepting payments from illegal gambling websites.

The US authorities also seized the internet addresses, one of which is run from the Isle of Man, another from Dublin and the third from a Commonwealth Caribbean country, where online gambling is legal. The move, seen as a serious escalation in an struggle between the US authorities and the online gambling industry which generates billions, caused outrage among British and international gamblers. Last month, Pokerstars' flagship event attracted nearly 60,000 players competing for prize money of $11.8m (£7.2m).

Pokerstars' owner Isai Scheinberg and the company's director Paul Tate, both Isle of Man residents, were accused of "deceiving United States banks" according to a US Justice Department spokesman. In a statement, prosecutors claimed this was done by "among other things, arranging for the money received from gamblers to be disguised as payments for hundreds of non-existent online merchants and other non-gambling businesses".

A spokesman for the US Attorney's Office said yesterday it was working with "foreign law enforcement" in the hope of extraditing defendants located abroad and seizing their assets.

Legal experts said the case would test US gambling laws. Critics say the law prohibits sports' betting but opinions are divided on whether it covers online games such as poker and blackjack.

UK gambling expert Simon Holliday, director of H2 Gambling Capital, warned the online gambling industry could face a massive confidence crisis. He said: "These sites are like banks. Players put down a deposit to play, and they have to be able to trust these sites. What happened with Northern Rock could happen here, because these sites have had their balances frozen by the US authorities.

"You have to bear in mind that 20 per cent of the players on the sites are money-making – it's their main source of income, like a career. There are some big deposits in there. You'll get lots of small-time gamers who have about £100 stuck in there at the moment. But then there are the big players, who could have tens of thousands in there.

"When these site owners have to pay money back, or if they're fined hefty amounts, they'll see if they can pay out of corporate funds. They probably won't be able to, and they'll think nothing of using their players' funds, just like the banks did. So just like what happened with banks, the players will probably only get a proportion of what they're owed.

"I would speculate that 500 to 1,000 players in the UK could lose anywhere in the region of £2,000, all the way up to £30,000. There will be even larger, high-end losses than that. Worldwide I would estimate about 10,000 professional players could lose very significant amounts of money. It takes about 24 hours to cash in money, but people can't get their money off these sites now. Even if players miraculously do receive the last of their poker cheques in the post, the question is, will they be able to cash them in?"