Victoria Police has admitted its officers falsified over 250,000 roadside breath tests over five years.

An investigation was launched last year after the Transport Accident Commission (TAC) alerted Victoria Police to “anomalies” in breath testing data.

The review of 1,500 preliminary breath test (PBT) devices and more than 17.7 million tests found over 258,000 PBTs, or 1.5 per cent of all tests, had been falsified.

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

The TAC usually contributes $4 million to Victoria Police each year, but has suspended its funding for the organisation while the investigation continues.

Professional Standards Command Assistant Commissioner Russell Barrett says police will get a talking to.

“We will commence the largest workplace guidance exercise undertaken in the Victoria Police,” he said.

“We'll be going out to every workplace and speaking to every member and explaining to them why this practice is wrong, what their roles are and why we need the trust and support of the community.

“We're going to ask why this has occurred so that we can learn from that and prevent repetitions of it.

“This behaviour tarnishes the reputation of all police officers.

“All police officers out there are doing a wonderful job at reducing trauma on our roads, they're reducing crime on our streets and are working incredibly hard to serve our community.”

Mr Barrett suggested 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.