THE racing corruption scandal has dramatically widened, with at least four top jockeys along with professional punters and other racing identities now under investigation.

In addition to the Smoking Aces scandal - which The Age can reveal involves fresh allegations that top jockey Danny Nikolic paid kickbacks to a third party to fix a race - authorities are also examining corruption allegations linked to several other horse races.

One of the allegations being probed involves one of Australia's most famous jockeys, who The Age cannot identify for legal reasons, who bet thousands of dollars on a rival horse to win a race in which the jockey was riding. The race was at a metropolitan Melbourne track within the past two years.

Meanwhile, a source from wagering company Betfair has confirmed a major investigation is being conducted into suspicious ''lay betting'' - in which a punter backs a horse not to come first - involving more than two dozen races and another leading jockey.