Victoria Police officers have raided the properties of top Australian harness racing figures over their alleged involvement in a race-fixing scandal.

The Monday morning raids have targeted the racing operations of the Cramp family in Mildura.

Shayne Cramp is one of the state's leading harness racing drivers, while both he and his father Greg also run a major training operation as well.

Fairfax Media was to publish an investigation about the pair's links to suspect betting activities and alleged corruption a fortnight ago, but was requested by police to stall publication.

The Fairfax Media investigation can reveal that Shayne and Greg Cramp are alleged to be involved in a suspected illegal betting syndicate that has been attempting to manipulate the outcome of races for several months.

No other members of their family are alleged to be involved.

The syndicate is allegedly involved in the manipulation of punting odds and driving practices in a manner that corrupts the outcome of betting.

The police investigation, carried out by detectives from the force's Sports Integrity Unit, has been running for at least 10 months.

Four properties in Mildura have been raided along with another property in Melbourne. Police have seized evidence.

Several prominent harness racing identities are expected to be charged with corrupting the outcome of a race or betting in what will be a major test of Victoria's relatively new 'cheating in sport' laws.

The raids are set to raise fresh questions about the integrity of racing in Victoria, with key insiders telling Fairfax Media that harness racing has been vulnerable to corruption due to the poor resourcing of the sport's integrity area.

Stewards have investigated Shayne and Greg Cramp in connection to several suspect races over the last few years but have failed to stop the pair's rise in running one of the most successful harness racing operations in the country.

The pair's operations were also investigated during the infamous 'blue magic' doping investigation in 2006, but stewards laid no charges.

The revelations come just weeks after three top thoroughbred trainers, Peter Moody, Danny O'Brien and Mark Cavanagh, were notified that some of their horses had tested positive for banned levels of cobalt after they raced in the spring carnival. The trio have pleaded their innocence.

Fairfax Media can also reveal that a prominent harness racing figure has been investigated by stewards over allegations they have been supplying cobalt to thoroughbred and harness racing stables across the state. It's understood this harness racing figure was raided and quizzed by stewards last year.

The state government recently ordered a major review of harness racing in Victoria due to falling revenue levels in the sport. The review, led by top racing administrator Dale Montieth, has commissioned sports corruption expert and former chief steward Des Gleeson to investigate concerns about the integrity of harness racing.

Fairfax Media recently revealed how a suspected organised crime syndicate, led by prominent harness racing owner Paul Sequenzia and which is linked to top trainers and drivers, has also been suspected of harness race fixing.

A trotting horse owned by Sequenzia tested positive for the banned drug EPO in 2009, although Sequenzia avoided any major penalties after several of his associates accepted responsibility for the doping.  Sequenzia recently owned Sushi Sushi, one of the most successful horses in the history of harness racing.

Fairfax Media is seeking comment from the Cramp family.