A parliamentary inquiry has heard Victoria Police often fails to properly investigate allegations of police misconduct or assault.

The state is holding a public inquiry to assess whether the Independent Broad-based Anti-corruption Commission (IBAC) and other bodies are properly equipped to investigate allegations of police corruption and misconduct.

Melbourne-based Robinson Gill Lawyers said on the first day of hearings that IBAC would refer about 90 per cent of complaints of misconduct back to Victoria Police, which creates “clear risk for a conflict of interest”, and proves the need for an independent investigative body.

It said its clients have been awarded compensation after Victoria Police investigators initially dismissed their claims as “unsubstantiated”.

“The current complaints system simply isn't working,” Robinson Gill’s principal lawyer Jeremy King told the inquiry.

“There is an inherent conflict of interest with police investigating themselves, and this is compounded with a lack of transparency.”

The lawyers also argued that police investigations tended to lack transparency.

It pointed to an IBAC audit in 2016 that found 16 per cent of people who made a complaint were not contacted by the officer investigating it, while 34 per cent of witnesses were not contacted.

Mr King said the situation was forcing people to report their claims to IBAC because they did not trust Victoria Police.

“IBAC is a corruption commission, not a complaint body,” Mr King said.

The union representing officers said Victoria Police had a strong track record in investigating and prosecuting officers.

“I'm not convinced that the system is broken,’ Police Association legal manager Chris Gorissen said.

“I'm also not convinced that the public has lost confidence in the current system. I'm yet to see any real, hard, fast evidence of that.”

The police union said IBAC’s powers did not need to be changed.

“We would call into question, with all due respect to people who work at IBAC, the skillset that's necessary to complete those investigations with real clarity and timeliness,” Mr Gorissen said.