Bookmakers have welcomed Gordon Brown's Budget announcement of a review of the way internet betting exchanges are treated by the tax system.
A taxation review was announced by the chancelllor in the Budget
Betting exchanges have soared in popularity with around 250,000 UK punters using them.
But High Street bookies complain they are not competing on equal terms because the exchanges only pay taxes on their relatively low commission.
They say betting exchange punters should pay tax on their winnings.
Unlike conventional bookmakers, betting exchanges allow punters to lay odds on horses and bet against each other.
But there has been concern that some people have been using inside information to rig the market.
The Jockey Club is particularly concerned that punters on betting exchanges can make cash out of horses losing.
Welcoming the review, William Hill spokesman David Hood said: "All that we are asking for is that anyone who lays bets on an exchange should be subjected
to the same regulation and taxation issue as any other licensed bookmaker.
"We would welcome any step forward that is made to address the imbalance that has been allowed to arise in what is traditionally the best-regulated gambling
industry in the world."
Ladbrokes said a review the tax treatment of betting exchanges and their clients was overdue.
"We have always maintained that layers - individuals who act as bookmakers - on exchanges enjoy an unfair tax advantage."
But Paul Cooper, of betting exchange Sportingoptions.co.uk, said they were already taxed fairly.
"All we want is to maintain a level playing field.
"Professional gamblers have not been taxed in the past and there's no way they should be taxed now because they're taking the position of saying something
will or won't happen.
"Layers are basically backing all the other horses in the race."
The British Horseracing Board has called for tighter regulation of betting exchanges.
They say the fact a punter can make a profit on horses losing threaten the integrity of the sport.