Underworld figure Mick Gatto has denied ever threatening to kill Informer 3838, as Victoria Police has previously alleged in court.

Key points: Mick Gatto says he is considering his legal options over the media reports

Mick Gatto says he is considering his legal options over the media reports Informer 3838 listed Mr Gatto as a "work in progress" among cases she had helped police with

Informer 3838 listed Mr Gatto as a "work in progress" among cases she had helped police with A senior police officer gave evidence that Mr Gatto had threatened to murder the lawyer

Confidential evidence of a senior police officer tendered in the Victorian Supreme Court states Mr Gatto had threatened to murder the defence lawyer and registered police informer, if it was ever proven she was speaking to police.

When initially contacted by the ABC, Mr Gatto refused to comment about the specific allegations contained in the court documents.

Today, Mr Gatto issued a statement via his lawyer refuting any suggestion he was a client of Informer 3838 or made any threats against her.

"Mr Gatto was never a client of Informer 3838. Not only is the reporting false, it is mischievous and damaging to Mr Gatto," the statement read.

"As a result, my client is considering his legal position."

Mr Gatto says he was never a client of Informer 3838. ( AAP: Julian Smith )

The ABC understands Informer 3838 was close to Gatto for at least four years after she started informally providing information to police.

Victoria Police spent more than $4 million on a legal battle that went all the way to the High Court in a bid to keep their use of Informer 3838 a secret, arguing her life would be in danger if the arrangement was made public.

Documents released by the Supreme Court included multiple affidavits outlining the risk posed to Informer 3838's life, including details of allegations made by police in relation to Mr Gatto.

Inspector Brooke Hall, an officer of more than 30 years' experience, stated in his affidavit that the risk to Informer 3838 came from "some of Australia's most notorious and violent criminals, who are proven to have organised murders in the past".

He stated that Mr Gatto, Horty Mokbel — the brother of Tony Mokbel, who Informer 3838 also claims credit for imprisoning — and others had threatened her.

Tony Mokbel's brother Horty was one of the people Informer 3838 claimed to have helped put behind bars. ( ABC News )

"That group specifically stated that if [Informer 3838] were found to be a human source then [she] would be killed," Inspector Hall said.

The ABC understands the defence lawyer's assistance to police about Mr Gatto related to evidence given by a witness in a trial implicating him in the murder of career criminal Victor Peirce, who was shot dead in his car in Port Melbourne in 2002, and the murder of fruit and vegetable wholesaler Frank Benvenuto, who was found slumped dead in his car in 2000.

"Mr Gatto was not charged with anything to do with their deaths," his lawyer, Martin Amad, said.

Frank Benvenuto was shot in the chest outside his Beaumaris home in May, 2000. ( ABC News )

Mr Gatto is one of the great survivors of Melbourne's underworld — a man who beat murder charges over the death of Andrew "Benji" Veniamin, escaped unscathed from multiple plots to kill him, including at his son's wedding, and even managed to build a significant fortune despite declaring bankruptcy in 1993 after a failed investment in a bomboniera business.

The only person convicted over the Peirce murder was getaway driver Faruk Orman, another associate of Gatto, who is now looking at launching a bid for freedom in the wake of the Informer 3838 scandal.

In a letter written by Informer 3838 released by the court, the former lawyer listed Gatto and the Carlton crew as a "work in progress" among the 10 most significant convictions or arrests she had helped police with.

Faruk Orman is serving a 20-year jail term for the murder of career criminal Victor Peirce. ( ABC TV )