The Sydney silk who led historic corruption inquiries into crooked former Labor kingpin Eddie Obeid has hit back at claims the anti-corruption commission is a "star chamber" that results in few prosecutions.

In a robust defence of the Independent Commission Against Corruption, Geoffrey Watson, SC, said complaints that reputations had been trashed by the organisation were "not to the point".

"Tell me the name of somebody whose reputation was trashed where it wasn't justified," he told a conference in Sydney on Wednesday. "I think you'll find it is a misplaced criticism."

The ICAC has come under fire this year as it switches its focus from Labor to Liberal figures, triggering the resignation of a string of state government MPs.

Mr Watson, who made clear he could not speak about inquiries that are not yet completed, said he heard the complaint that the ICAC was a "kangaroo court or a star chamber" every day.

Corruption was "inherently hard to prove" because it was "something people tend to keep secret," he said.

This justified the "extraordinary" powers that were given to the commission, which extended beyond those that could be exercised by the police or the courts.

He said the commission was "very, very, very careful with them".

Mr Watson added it was "not factually accurate" to say the work of the organisation was "futile because of few prosecutions".

"There are lots of prosecutions," he said. "But even if there weren't – so what? Look at what ICAC achieved."

Mr Watson said Operation Jasper, the high-profile inquiry into a lucrative coal tenement created "smack bang on top" of the Obeid family's farm in 2008 by then Labor mining minister Ian Macdonald, exposed corruption worth tens of millions of dollars.

As a result of the investigation, laws had been passed to expunge a coal exploration licence that was "born under a cloud of fraud".

"Do you think it would be better if that inquiry had never been conducted?" he said.

Mr Watson also gave a glimpse into the painstaking investigations conducted by the ICAC before it held public inquiries.

The ICAC was "much more like a detective agency" than a court, he said, and Operation Jasper had been triggered by a tip-off from a convicted criminal who was trying to get "moved to a better jail".

He said that witnesses were often "reluctant to tell the truth" and at times the investigation was akin to "thrashing about in the dark".

While it was the lawyers who "hogged the glory" in newspapers and on TV, Mr Watson said it was the forensic accountants who were the "heroes" of Operation Jasper. The work required an eye for detail, diligence and patience - in some cases for years on end.

"It was like a spy story, but it would not translate well to the screen," he said.