Detective Senior Sergeant Tim Argall - among the first officers to deal with the criminal lawyer in the mid-1990s - says at one point she was so enthusiastic she made up a fictional name for a covert operative and officers had to "run with it".

After first trying to tip off police to a man buying illegal guns she then turned on her former lover Brian Wilson, with allegations of drug trafficking leading to an undercover operation, Sgt Argall told a royal commission into police use of informers on Monday.

Retired assistant commissioner Jack Blayney was in charge of the undercover unit at the time and went on to call Ms Gobbo a "loose cannon".

Senior Sgt Argall said in one instance she told Wilson the name of a character to be played by a covert agent, before the police operation and without permission.

"She had done that without any consultation from us and I think that had caused a degree of angst," the detective said.

"She just plucked a name and we had to run with it."

Counsel assisting the commission, Chris Winneke QC, suggested Ms Gobbo was "getting into the spirit and enjoying the process".

Senior Sgt Argall's association with Ms Gobbo continued socially and in 1997 there was what Mr Winneke described as an "episode of physical intimacy".

He also took her to a police ball and attended other social events.

Inappropriate relationships between Ms Gobbo and police officers have been raised in the commission.

Senior Sgt Argall maintained contact through the years and was seeing her monthly through 2003 and 2004.

Former drug squad detective Paul Dale was also seeing her socially at the time, he said.

Ms Gobbo's barrister Rishi Nathwani suggested to Sen Sgt Argall that police sometimes logged tips from her as Crime Stoppers reports or through search warrants on the then-barrister's chambers to protect her identity.

He denied knowledge of both.

Former assistant commissioner Jeff Pope, who was Ms Gobbo's handler in 1999, took to the stand on Monday afternoon saying in his "very vague recollection she was very keen to assist and seemed to be reliable".

Mr Pope was in the middle of a law degree at the time he signed her and admitted knowing she was a barrister, but said he wasn't sure he was aware of her duties of confidentiality and legal professional privilege.

Ms Gobbo was registered a third time between 2007 and 2009 while representing some of the most prominent figures in Melbourne gangland war, including Carl Williams and drug lord Tony Mokbel.

Detective Inspector Gavan Segrave, who endorsed Ms Gobbo's 1999 informer registration, earlier revealed he had made a conscious decision to hide his prior involvement with her when advising an assistant commissioner for a legal case around her third recruitment in 2010.

Australian Associated Press