An Australian lawyer who defended gangland bosses has been unmasked as a police informant. The revelation could result in a huge number of criminal convictions being overturned.

The Melbourne barrister, who cannot be named, defended crime bosses including notorious drug lord Tony Mokbel and six of his associates. She double-crossed her mobster clients between 2005 and 2009 by covertly handing over sensitive information on the cases to the Victoria police. The intelligence was used to assist the prosecution in over 380 cases, including the trial of Mokbel in 2012 which resulted in him being sentenced to 30 years in prison.

The secret operation was leaked, but the police and the barrister initially managed to obtain an injunction to suppress the details. However, the High Court in Australia has now lifted the injunction saying the lawyer's role as an informant was a "fundamental and appalling breach" of her professional obligations. The court also lambasted the police for being "guilty of reprehensible conduct". It added that the prosecutions against the convicted individuals were "corrupted" in a way which "debased fundamental premises of the criminal justice system". As well as facing the wrath of the court, the barrister is likely to be feeling uneasy at the prospect of mafia ex-clients discovering that she dobbed them in.

According to reports in Australia, hundreds of cases could be reviewed as numerous convicted criminals who were represented by the lawyer will be notified that they could potentially appeal against their convictions. 

Daniel Andrews, Premier of the state of Victoria, said that an inquiry would take place as the public had a right to know that the justice system "acts fairly and lawfully at all times". 

A spokesman for the Victoria police said that Melbourne had been "in the grip" of gangland wars, and defended the use of the informant due to the "significant" risk to the community at that time. So never mind about any expectation of a fair and honest defence. He added that the police would cooperate fully with the inquiry.