A bill before State Parliament will make it harder for the Independent Broad-based Anti-corruption Commission to hold public hearings, depriving the corruption fighters of a key weapon in their armoury against crooked cops, public servants and politicians.

Stephen Charles, QC, who chaired the panel that advised the Baillieu Liberal government on IBAC's set-up, says public hearings were important in cases against allegedly corrupt public servants and police officers who bashed detainees.

Mr Charles, a former Supreme Court judge, says it is vital the commission is not weakened further.

His call has been backed by think tank The Australia Institute, which says IBAC is weak compared to the anti-corruption bodies of Western Australia, Queensland and NSW. Those bodies' investigative abilities are as powerful as a full royal commission.

The institute says IBAC has narrow limits on what it can investigate and its power to search premises, call witnesses, hold hearings, and gather and hold evidence, and that the bill before Parliament means the state’s watchdog is in danger of losing some of the few teeth it does have.

The office of Special Minster of State Gavin Jennings, who is driving the reform bill, did not respond to a request for a comment before deadline on Monday.

Mr Charles told The Age that the bill allowed suspects to potentially avoid public hearings if they could show it might damage their reputation, health or safety.

“Any suspect who is in a public hearing and is being cross-examined will almost certainly make an application to have the public hearing held in private,” the former judge said.

“If the IBAC commissioner refuses the application, then there’s likely to be an appeal to the Supreme Court and there could be an appeal to the Court of Appeal."

Mr Charles said the public hearings into the conduct of corrupt senior public servants at the Department of Education and Training were vital to the success of the case.

“It made the community aware of what was taking place immediately and the result was the Education Department immediately taking measures to stop this happening again, it resulted in a lot of complaints coming into the IBAC about possible corrupt conduct,” he said.

“If you didn’t have those public hearings, the public wouldn’t get to hear about it until possibly years later when a report was made to government.”

The cases of misconduct by police officers stationed at Ballarat was also important, Mr Charles said, after two of the accused fought all the way to the High Court in a unsuccessful effort to have the proceedings held behind closed doors.

Mr Charles said the experience in other jurisdictions had also underlined the importance of anti-corruption commissions holding public hearings.

“All of the anti-corruption commissioners believe these public hearings are an important tool in their powers,” he said.

“There is the possibility of damage to reputations but that happens in almost all law commissions you can think of.

“Damage to reputation is reduced if there is thorough investigation beforehand and they know they have a pretty strong case against the people they’re investigating.”