Broadcaster Alan Jones has told a defamation trial he had no hydrological evidence to support claims he made on air that the collapse of a quarry caused the deaths of 12 people in the Grantham floods.

The Wagner family from Toowoomba is suing Jones in the Supreme Court in Brisbane, claiming he implied they were responsible for the deaths because they owned the quarry.

They also claim Jones suggested in broadcasts that they stole airspace for their privately built Wellcamp Airport at Toowoomba, and that it was corruptly approved.

The court was previously told the Grantham Floods Commission of Inquiry exonerated the family of any responsibility for the deaths.

Jones told the court on Monday he didn't accept the findings from the inquiry's commissioner Walter Sofronoff QC.

"My concern was the hydrology reports were not correct, not accurate, and therefore while I accepted what Mr Sofronoff has said, I didn't accept the conclusions," Jones said.

Under cross-examination by the Wagners' lawyer Tom Blackburn QC, Jones maintained his belief that the quarry was responsible for the deaths.

Jones told the court: "I've said that many times, that's not news".

Mr Blackburn asked: "You had no hydrological evidence when you made this statement of fact on this day?"

Jones replied: "No, I did not".

The radio broadcaster told the court he was acting as "a voice for the voiceless" and his comments were based on his gathering of information from long-time Grantham residents.

Jones told the court, "I have plenty of eyewitness evidence."

"These people were victims of a horrific disaster, I consulted with them like no-one else had, I believed the stories they were telling me.

"I strongly worded my concerns … and I hold them today."

After three days of evidence, the Wagner's lawyer finished his cross-examination with a fiery exchange with Jones.

"You put the Wagners under siege didn't you, in your succession of radio broadcasts?" Mr Blackburn said.

Jones replied: "Not at all. I just tried to deal with the facts as I saw them."

Mr Blackburn: "Your attacks on them were arrogant."

Jones: "No."

Mr Blackburn: "Vicious."

Jones: "No."

Mr Blackburn: "And baseless."

Jones: "No."

'You likened it to bribery, didn't you?'

Earlier in the day, Jones was questioned about an email exchange in 2014 with Qantas CEO Alan Joyce, to have the airline set up operations at the Wagners' private airport on the Darling Downs, west of Brisbane.

The court heard Mr Joyce wrote to Jones that the Wagners' offer to Qantas was "commercially very attractive" and one its competitor would have taken if provided the opportunity.

Jones told the court: "It wasn't an orthodox commercial agreement."

Mr Blackburn asked: "On the basis that you say you thought the arrangement was unorthodox, you likened it to bribery didn't you?"

Jones replied: "Well, I think I used that word somewhere. I mean if you offer an inducement to someone to do something, what word do you use?"

The broadcaster denied he was trying to "bully" Mr Joyce to reject the Wagners' airport.

"You were trying to convince or persuade Mr Joyce not to fly into the airport," Mr Blackburn suggested.

"Not at all," Jones replied.

The court heard Jones also approached Virgin chief executive officer John Borghetti about concerns he held over the approval process of the Wellcamp Airport.

"I would have emphasised that it was a very corrupt process," Jones said.

"... I didn't expect any gratitude but I think they were appreciative of the statements I made."

The Wagners are seeking $4.8 million in damages from Jones, Harbour Radio, 4BC and journalist Nicholas Cater.