A further five lawyers may have acted as police informants, the ABC understands, as it emerges that the lawyer whose role as a Victoria Police informant sparked a royal commission was registered as an informant 10 years earlier than previously disclosed.

Key points: The commission has been told the informant was first registered in 1995, not 2005 as previously understood

The commission has been told the informant was first registered in 1995, not 2005 as previously understood The scope of the commission will be broadened to include the use of other informants, including some lawyers

The scope of the commission will be broadened to include the use of other informants, including some lawyers A commissioner whose time at Victoria Police overlaps with the use of the informant has stepped down

The revelations have the potential to bring many more criminal convictions into question, and have prompted the resignation of Commissioner Malcolm Hyde from the royal commission.

Mr Hyde stood down because of the "overlap between the matters of interest and Mr Hyde's time at Victoria Police", not because of any direct conflicts of interest, Attorney-General Jill Hennessy said.

Ms Hennessy also said it had been discovered police had used "further informants who held obligations of confidentiality", including other lawyers.

The ABC understands there are six lawyers who acted as informants.

In a brief statement, Victoria Police blamed the incorrect information about the timing of the informer's work with police on "shortcomings" in its record-keeping practices during the mid-90s.

The royal commission was set up to investigate Victoria Police's use of the defence lawyer, known as Informer 3838 or Lawyer X, as a registered police informer during Melbourne's bloody gangland wars.

The Office of Public Prosecutions last year wrote to 20 convicted criminals, including drug kingpin Tony Mokbel, to inform them of the lawyer's role as a police informer in their cases, believing that those people could move to have their convictions quashed.

Underworld figure Tony Mokbel may attempt to have his convictions quashed. ( AAP: Julian Smith, file photo )

'Reprehensible conduct'

The High Court has described police's use of the lawyer as "reprehensible conduct" which involved sanctioning "atrocious breaches of the sworn duty of every police officer".

The court also found the defence lawyer had engaged in a "fundamental and appalling breach" of her obligations as a barrister.

Ms Hennessy said commissioners had recently been told by Victoria Police that Informer 3838 had been first registered in 1995, not 2005 as previously stated in High Court documents.

"There are [also] some other informants who have been identified who are lawyers, I'm not going to speak to the detail of those issues but there are some others that have been identified," she said.

Victoria Police said the 10-year difference in dates was discovered while police were preparing information for the royal commission.

"The information had not previously been identified due to shortcomings in our record keeping practices related to informers in the mid-1990s," the statement said.

"These practices have since been comprehensively improved. Victoria Police is committed to cooperating fully and transparently with the Royal Commission to aid in its inquiries.

"Accordingly, on establishing this important information we took steps to ensure the Royal Commission was informed."

Ms Hennessy said the terms of reference for the royal commission, due to report later this year, would now be broadened.

Malcolm Hyde served as the commissioner of South Australia Police for 15 years. ( ABC News )

Ms Hennessy said Mr Hyde, a former South Australian police commissioner, was satisfied there were no direct conflicts of interest but he wanted to avoid any adverse perceptions about the royal commission's impartiality.

Mr Hyde's police career began with Victoria Police in 1967, where he served for 30 years, reaching the rank of deputy commissioner in 1994.

He was appointed commissioner of South Australia Police in 1997, a role he retired from in 2012.

What does it mean?

Sorry, this video has expired Jill Hennessy said police had revealed new information to commissioners.

Last year, it was revealed Informer 3838 worked for police from September 2005 until January 2009.

But it was also revealed she met with detectives from the Purana Taskforce, which was investigating the gangland wars, to give them "valuable information" in 2014.

The informant — whose identity cannot be reported — has claimed 386 arrests and convictions were made due to her help in that time period.

Previously, Victoria Police agreed to a statements of facts before the Supreme Court that the informant was registered on September 16, 2005.

Asked by reporters why Victoria Police had not revealed the true depth of the legal scandal, Ms Hennessy said that was a question for police to answer.

"It was initially the anticipation that the Royal Commission would investigate the matters around the informer at the centre of this matter," she said.

"In the course of the commission's early work, there's been a number of issues that have been disclosed and they will be identifying those other issues."

Victoria Police spent $4.5 million on a legal fight to keep their arrangement with Informer 3838 a secret due to fears she and her family would be murdered.

The Government said it would consider a possible time extension for the commission in the wake of the new information.

In a statement, royal commission chair Margaret McMurdo thanked Mr Hyde for his work as a commissioner.

"I sincerely thank him for his contribution to the administration of the Commission, for his integrity, and for his commitment to the best interests of the Commission, the criminal justice system, and the public," she said.

Ms McMurdo said public submissions to the commission would be able to be made soon through the royal commission's website.

Full statement from Jill Hennessy: