Former NSW treasurer Michael Costa's nickname for his colleague Tony Kelly was "the Jed Clampett of Parliament", according to the memoir of their former colleague Frank Sartor.

The comparison with the star of the Beverley Hillbillies was as much to do with Kelly being a rural MP as Costa's view of him as not the sharpest member of the cabinet.

In the witness box at the Independent Commission Against Corruption on Thursday, Kelly did little to challenge that perception.

Accused by counsel assisting Geoffrey Watson, SC, of being complicit in the creation of a "fake" cabinet minute that would have benefited Australian Water Holdings, a company associated with Labor powerbroker Eddie Obeid, Kelly vehemently denied it.

But in the course of doing so, he offered a somewhat alarming insight into how he operated as a member of the former Labor government.

Kelly admitted that he "knew nothing about the detail" of the company he was putting forward to cabinet as a potential supplier of infrastructure in Sydney's north-west.

He agreed he had no idea of how many employees or resources it had, or if it had a structure "beyond that of a $2 company".

The best Kelly could offer was: "I knew they had provided water in western Sydney" but couldn't recall speaking to anyone at Sydney Water as to their performance. He relied on information from his staff but didn't know where they got it from.

"What sort of things go on in Macquarie Street in a minister's office if you do not know the source of information upon which you are relying?" Watson asked incredulously.

"What's going on in there?"

Perhaps Costa's jibe wasn't far off the mark after all.