Betting exchanges are under scrutiny by MPs, keen to protect punters and improve the integrity of sports betting.
BBC Sport looks at the issues surrounding betting exchanges and examines the implications.
WHAT ARE BETTING EXCHANGES?
They are online betting sites that have rapidly developed over the past three years where punters can bet against each other.
In racing, punters can either back a horse to win or "lay" a bet that a horse will lose at their chosen odds.
So in football you could have put £10 on Greece to win Euro 2004 at 500/1 and then lay them at 2/1 in the days before the final - ie bet against them winning the competition - in order to guarantee a profit either way.
The exchange acts as a broker, matching the punter with the layer, and takes a commission for this service.
WHAT ARE THE ADVANTAGES?
Punters get the choice of betting in the normal way or playing bookmaker, controlling their odds.
Exchanges can also provide the opportunity to allow punters to bet "in-running" - after the event has started.
SO WHY ARE THEY CRITICISED?
Racing bosses are concerned that betting exchanges represent a threat to the integrity of the sport, something other groups including European football's rulers Uefa are worried about too.
Former British Horseracing Board chairman Peter Savill was a fierce critic.
"Betting exchanges have suddenly enfranchised 30m-plus people in Britain to make money out of horses losing a race," he said.
"When you add to that figure every other person in the world with the desire to make money out of horses in Britain losing races - including, possibly, illegal bookmakers and even organised crime - you have to wonder whether the decision [to allow franchises] was reached after appropriate research."
WHAT DO THE EXCHANGES SAY?
They insist exchanges have increased the transparency in betting activities through the signing of various memorandums of understanding with sport governing bodies, including the Jockey Club.
Under the agreement, exchanges pass on information relating to unusual or suspicious betting patterns to officials.
Rob Hartnett, a spokesman for betting exchange Betdaq, highlighted the ability to provide a paper trail of the activities of members.
"With an online exchange, there is a record of every bet struck, and all the betting exchanges have worked with the Jockey Club and other sporting authorities to make sure that the sport is run properly and cleanly," he said.