The US is nearing a watershed moment. The supreme court is considering whether to repeal PASPA after a protracted legal challenge by the state of New Jersey – and the signs are that New Jersey will get its way.

 “This is the closest the US market has come to opening up,” says Kip Levin, the chief executive of the US business at Paddy Power Betfair. “The sports leagues and the casino industry are behind it, so all the winds are blowing in the right direction.”

A decision is expected any time between now and the end of June, which could open up a vast business opportunity for those quick enough to seize it. With the prize on offer so great, Britain’s bookmakers are already jockeying for position. They have years of experience because of Europe’s more liberal approach to sports gambling, while sharing a common language reduces barriers to entry.

William Hill already holds a commanding position. It owns a sizable operation in Nevada, where sports betting is permitted, operating more than half the casino sportsbooks there.

It also has a betting operation ready to go in New Jersey in partnership with Monmouth Park racecourse and says it could be ready to take bets “within days”. The firm is in negotiations with potential partners in several states and believes the US could eventually become its most profitable territory.

“Nobody is going to benefit more than William Hill in that market,” Darin Oliver, a gambling industry consultant and former deputy director of the Alderney Gambling Control Commission, says.

He points out that the federated legal architecture of the US means a repeal of PASPA would not lead to nationwide sports gambling overnight.

“The states still have to pass legislation and that won’t happen immediately. California, one of the biggest markets, is at least a year or more away from allowing it, if they even do,” Oliver says.

“The New Jersey concession means William Hill will benefit immediately.”

Oliver believes the potential of the US market is one reason why the hedge fund Parvus, the largest shareholder in William Hill, has been instrumental in scuppering two mergers, one with Canada’s  The Stars Group and the other a three-way tie-up with London-listed Rank and 888.

Hargreaves Lansdown, thinks the timing may prove difficult.

“If you look at the chain of acquisitions going on there already – Coral merged with Ladbrokes, Ladbrokes being bought by GVC, there’s a lot going on internally.

“So what appetite there would be there I don’t know. They may have enough on their plate.”

Salmon says the US could be a plentiful frontier for Britain’s bookies but not without pitfalls.

“It would obviously be a huge opportunity if it gets opened up. Think about the fact that people drive from all over to go to Las Vegas. It tells you something about the appetite.

“How it would open up is another question and you’d need the dominoes to fall in the right order. You’d have to sink a lot of money in initially. So you wouldn’t be square that quickly.”

Oliver, who has decades of experience with the US gambling environment, points out that the illegal sector would not necessarily disappear either.

“I think they were holding out for a better price and the only way out for them was a US PASPA ruling.”

If William Hill is a nose in front of the rest, Paddy Power Betfair is coming up on the rail. It already has 300 US staff and owns the TVG television network showing live horse racing, which benefits from an exception to PASPA.

It could use this as a launchpad to promote sportsbooks across the US by setting up partnerships with racecourses and casinos, likely to be the gateways to a licence under most of the terms being drawn up by states.

“We’ve been operating in New Jersey through our casino business, so we’re a known entity there,” Paddy Power Betfair’s Levin.

“To operate sports betting would be an extension of that. We’d then have to figure out the tech strategy, which we’re already spending time on.

“The big unknown is how quickly the market will expand as it opens up state-to-state. Our intention is we’d be ready from a tech standpoint by the fall.

“We have a lot that will help us whereas some other European operators without much of a business here will have to invest a lot.”

Ladbrokes and GVC, soon to complete their £4bn merger, have a small US presence but do possess the combined experience, as well as the systems and technology, to dive into a liberalised market.

However, George Salmon, a gambling equity analyst at the stockbroker Hargreaves Lansdown, thinks the timing may prove difficult.

“If you’re already betting with your illegal bookmaker, do you switch? There are a lot of studies on this and the general consensus is that the illegal business will continue.”

While few expect the supreme court to leave things as they are, an almost equally dissatisfying outcome for the bookmakers is that, rather than repealing PASPA, it simply decriminalises sports betting in New Jersey alone.

That would likely trigger a wave of further legal action from states, muddy the waters even further, and postpone indefinitely the British bookies’ big chance to break the US.