A number of criminals could launch legal bids for freedom as a result of a secretive case of high-level police misconduct involving a defence barrister-turned-police informer during Melbourne's bloody gangland war.

Key points: Lifted suppression orders reveal a barrister who represented gangland figures gave information on their clients to police

Lifted suppression orders reveal a barrister who represented gangland figures gave information on their clients to police Covertly informing on clients was a "fundamental and appalling breach" of the barrister's obligation, the court found

Covertly informing on clients was a "fundamental and appalling breach" of the barrister's obligation, the court found The revelations are being considered by the Victorian Government which is meeting for the first time since the election

Court documents reveal the lawyer claimed to have helped police in as many as 386 cases, including that of notorious underworld figure Tony Mokbel, which could result in appeals from criminals applying to have their convictions quashed or sentences slashed.

At 9:00am (AEDT), suppression orders were lifted on a case decided in the High Court last month involving Victoria Police and the lawyer who represented numerous gangland figures, against the Victorian Director of Public Prosecutions.

The High Court judgement condemned Victorian police saying they were guilty of "reprehensible conduct" in encouraging the barrister to give up information about the accused and were involved in sanctioning "atrocious breaches of the sworn duty of every police officer".

"As a result, the prosecution of each convicted person was corrupted in a manner which debased fundamental premises of the criminal justice system," the court said.

Court documents revealed that the barrister, who represented Tony Mokbel and six of his associates, was also acting as a paid informant against her clients, and passing information about them to Victoria Police.

In 2015, after Mokbel and his associates were convicted, the Independent Broad Based Anti-Corruption Commission (IBAC) prepared a report for the Director of Public Prosecutions (DPP), recommending that it "consider whether any prosecutions had resulted in a miscarriage of justice as a result of the conduct of a barrister acting for those persons".

Police ruled risk of death to barrister was 'almost certain'

The DPP decided there was a duty to inform Mokbel and his associates that the barrister had given information to the police about them at the same time as she was acting for them.

The barrister — who cannot yet be named — also gave information to police about other clients she was acting for.

Those clients later made statements against some of the Mokbel group.

In the months that followed, Victoria Police undertook an assessment of the risk to the barrister if the DPP was to disclose the information to Mokbel and his associates.

Mokbel was arrested by police in Greece after leaving the country while he was on bail. ( ABC News )

The conclusion reached was that, if the information was disclosed, the risk of death to the barrister would become "almost certain".

On that basis, the then-chief commissioner of police and the barrister asked the court to restrain the DPP from making the disclosures, arguing that it would place the barrister and their family at "extreme risk of death or other harm", and "deter future informers from giving confidential assistance to police".

They lost the case, then lost again in the Court of Appeal, which found that the judge had properly taken account of the risks to the barrister and her family, and also the risk of deterring future informers.

The court found that the risks were outweighed by "the public interest in the right to a fair trial with the assistance of independent legal advice".

Last month, the High Court denied a final attempt to stop the DPP from providing the information to Mokbel and his associates, and revoked special leave to appeal.

In its judgement, the High Court accepted that "there is a clear public interest in maintaining the anonymity of a police informer".

However, the judgment also states that this situation is "very different, if not unique, and it is greatly to be hoped that it will never be repeated".

Lawyer involved in hundreds of cases

The court found that by covertly informing against her clients, while purporting to act as their defence lawyer, the barrister had committed "fundamental and appalling breaches" of her obligations.

The court accepted the magnitude of the risk to the barrister and her family, but noted that the barrister had declined to enter the police witness protection program, "taking the view that Victoria Police cannot be trusted to maintain confidentiality".

"If [the barrister] chooses to expose herself to consequent risk by declining to enter into the witness protection program, she will be bound by the consequences," the judgement said.

The lawyer claimed the information provided helped police in hundreds of cases.

"There were a total of 386 people arrested and charged that I am specifically aware of based upon information I provided to Victoria Police but there are probably more because as you would know, I did not always know the value or use of some of the intelligence that I was providing," the barrister said in a letter to police command.

The cases included convictions over the country's largest ecstasy haul, in which more than four tonnes of ecstasy was hidden in tomato tins, and other cases involving the "Mokbel clan".

Each of the barrister's clients will be sent a letter informing them that their lawyer was providing information "about you, in a possible breach of legal professional privilege and/or in breach of a duty of confidentiality," court documents revealed.

Tony Mokbel was sentenced to 30 years in prison in 2012 for masterminding an elaborate drug syndicate known as The Company.

He was arrested in Greece in June 2007, 15 months after fleeing Melbourne while on bail during a trial on cocaine importation charges.

In 2014, Daniel Andrews, who was the opposition leader at the time, refused to rule out holding a royal commission in a bid to restore faith in Victoria's justice system.

It is likely a Supreme Court judge will be appointed to review the cases to see if tainted intelligence or evidence was used to secure convictions or pressure people to plead guilty.

In 2015, a corruption watchdog investigation led by former Supreme Court judge Murray Kellam recommended the DPP consider if any convictions were compromised by police wrongdoing.

More than 30 people from rival underworld factions were killed during Melbourne's gangland war that raged between 1998 and 2010, as a result of a feud between drug kingpin Carl Williams and the Moran family.

Williams was himself clubbed to death by another inmate with the stem of an exercise bike in Barwon Prison in 2010.