Betting exchanges have hit the headlines in the wake of allegations surrounding the controversial defeat of a horse ridden by champion jockey Kieren Fallon.
Unusual exchange activity was reported to the Jockey Club before the race at Lingfield in which Fallon failed to ride out after leading by 10 lengths, enabling another horse to win.
Fallon, who was suspended for 21 days for the offence, says he simply made a mistake and strongly denies any wrongdoing. But what exactly was the unusual activity on the exchanges?
BBC Sport looks at the issues surrounding gambling's newest phenomenon and examines the implications for the world of racing.
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.
Punters can either back a horse to win or "lay" a bet that a horse will lose at their chosen odds.
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 also provide the opportunity to allow punters to bet "in-running" - after the race has started.
SO WHY ARE THEY CRITICISED?
Racing bosses are concerned that betting exchanges represent a threat to the integrity of the sport.
British Horseracing Board chairman Peter Savill said recently: "Betting exchanges have suddenly enfranchised 30m-plus people in Britain to make money out of horses losing a race.
"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 Far East 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 that they have increased the transparency in betting activities through the signing of the Memorandum of Understanding with the Jockey Club in June, 2003.
Under the agreement, exchanges pass on information relating to unusual or suspicious betting patterns to the Jockey Club.
It was the betting exchange Betfair that alerted the Jockey Club ahead of last Tuesday's race at Lingfield.
WHAT ACTION DOES THE BHB WANT TAKEN?
"The current law, which did not envisage the creation of exchanges, is now deficient and must be tightened in the forthcoming Gambling Bill as a matter of urgency," says BHB chief executive Greg Nichols.
"Government must change the law to empower the new Gambling Commission to operate with strong powers of investigation and sanction."
Nichols wants the following:
A distinction to be made between recreational and non-recreational layers on a betting exchanges.
This should, he says, be judged by the size and/or frequency of their laying over a specific period.
Non-recreational layers would be deemed to be in the business of betting and would require an appropriate licence, awarded on the basis of a "fit and proper" test.
The Gambling Commission should be given powers of investigation and audit to uncover abuse.
The Commission should be given sufficient powers to deter wrong-doing including, but not necessarily limited to, the withdrawal of licences from non recreational users.