Victoria Police has had $4 million of road safety funding suspended after an investigation revealed officers falsified more than 250,000 roadside breath tests in the state over a five year period.

Key points: More than 258,000 preliminary breath test falsified

More than 258,000 preliminary breath test falsified TAC suspends $4 million in road safety funding

TAC suspends $4 million in road safety funding Former chief commissioner Neil Comrie to investigate issue further

The Transport Accident Commission (TAC) alerted Victoria Police to "anomalies" in preliminary breath testing data last year before a police internal investigation uncovered fake testing was "widespread".

It found that officers were placing a finger over the straw entry hole of breath testing equipment, or blowing into the straw themselves.

The results of breath tests conducted on the public were not affected, police said.

After reviewing 1,500 preliminary breath test (PBT) devices and more than 17.7 million tests conducted over five years it found more than 258,000 PBTs, or 1.5 per cent of all tests, had been falsified.

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."

It is believed the fake tests were largely made by general duties and highway patrol officers, particularly in rural areas.

There is no suggestion officers misused breath testing devices while working at supervised drug and alcohol buses.

Mr Barrett said former police chief commissioner Neil Comrie would be appointed to look into the issue further.

"We're going to ask why this has occurred so we can learn from that and prevent repetitions of it and like practices in the future," he said.

Mr Barrett said Victoria Police was working with the TAC to "give them assurance".

"Our reputation's tarnished in the eyes of TAC and in the Victorian community. We can't walk away from that," he said.

TAC chief executive Joe Calafiore said he was supportive of the investigation to "get to the bottom of it".

"I think anything that has the potential to undermine confidence in what we do in road safety is a concern, and I share police's disappointment in what we've seen," he said.

Officers may have made false tests to 'highlight productivity'

Mr Barrett said he believed officers may have falsified the tests to meet targets.

"The question we all asked was why? There could be a number of reasons but the main rationale I believe is to hide or highlight productivity. Whatever reason our workforce may come up with, it isn't acceptable," he said.

He said there was no evidence to suggest officers had committed fraud, or any criminality has occurred.

"Similarly, there is nothing to suggest that any of this activity has impacted on any prosecutions," he said.

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

The investigation found 1.5 per cent of all tests had been falsified over five years. ( ABC News: Margaret Burin )

He said no individual members had been spoken to about the falsified tests, but all officers would need to attend a "guidance" session.

Police Association secretary Wayne Gatt said the finding was disappointing but highlighted the need for more resources.

"It comes as little surprise that when unrealistic targets are placed on our members that this sort of thing might emerge," he said.

Culture allowing fake tests 'deeply concerning'

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

IBAC commissioner Robert Redlich, QC, said evidence of a culture that allowed fake tests to occur over time without being detected was "deeply concerning".

Mr Redlich said he was concerned that no police officers reported the misuse of breath test devices.

"Victoria Police officers have a clear obligation not to turn a blind eye to any police misconduct, and to report it to Victoria Police or to IBAC so it can be thoroughly dealt with," he said.

Police Minister Lisa Neville said the false testing was unacceptable and "some action" should be taken.

"It has really breached trust with the Victorian community, but also breached the trust of those members who do the right thing," she said.

She said she had "complete confidence" in Chief Commissioner Graham Ashton and senior police managers to deal with the issue.