Victoria Police has had $4 million of road safety funding suspended after officers were found to have falsified more than 250,000 roadside breath tests over a five year period in an apparent attempt to fool productivity checks.

An exhaustive audit by Professional Standards Command and statisticians was launched after claims the officers were cheating the tests emerged late last year.

Officers were conning the tests by placing a finger over the straw entry hole or blowing into the straw themselves.

“The investigation, which analysed over five years of data, 1500 preliminary breath test devices and more than 17.7 million tests, disappointingly found 258,463 PBTs or 1.5 per cent of all tests had been falsified,” Assistant Commissioner Russell Barrett said.

“I had not heard of our members engaging in such a practice, we let ourselves down, we’ve let the community down. It stops now.”

Professional Standards Command assistant commissioner Russell Barrett said the TAC had put $4 million of road safety funding on hold.

“This practice will stop and stop immediately,” he said.

“From today on, this practice will not be tolerated.”

“We’ve let ourselves down, we’ve let the community down, we’ve let our road safety partners down.”

An external investigator will now be brought in to reveal why it happened.

The main culprits were general duties and highway patrol officers, according to the audit. Photo: AAP

“There could be a number of reasons but the main rationale I believe is to hide or highlight productivity,” Mr Barrett said.

“Whatever reason our workforce may come up with, it isn’t acceptable.”

The main culprits were general duties and highway patrol officers, with some rural areas over-represented.

The practice was not found at supervised drug and alcohol bus test sites and there is no evidence at this stage to suggest fraud or any criminality had occurred, or prosecutions were risked, Mr Barrett said.

Mr Barrett said more oversight of preliminary breath testing would be put in place.

He said all officers would also need to attend a “guidance” session.

Victoria Police said it was in contact with the Independent Broad-based Anti-corruption Commission (IBAC) about the issue.

Statisticians had to look at complex algorithms together with considerations on the length of time it would take to administer one test and a succession of tests.

The external investigator will also look at underlying cultural and behavioural issues, supervision and management practices that let the fake tests go unchecked, and aggravating circumstances that may need further investigation.

-with AAP