Former prime minister Kevin Rudd has refused to swear on oath at an insulation royal commission, claiming he isn’t able to tell the whole truth.

Former prime minister Kevin Rudd says he’s being gagged from telling the truth about Labor’s home insulation program, which led to the deaths of four young men.

Mr Rudd is refusing to swear on oath at a royal commission into the scheme, claiming his evidence shouldn’t be censored under cabinet confidentiality rules.

The startling move came after former environment minister Peter Garrett told the inquiry he was “gutted” by the first fatality under the $2.8 billion scheme, which was described in the commission as having attracted “shonks”.

Mr Rudd’s lawyer, Bret Walker, SC, on Wednesday argued the former Labor leader should be able to give a full and frank account of his involvement in the program, including what happened in the cabinet room.

Mr Walker also took a swipe at the Coalition government which defied a century-old convention by providing cabinet documents to the $20 million inquiry.

He says Mr Rudd should have the same right to be able to defend himself against claims he operated a failed insulation scheme and called for his unredacted statement to be made public.

But commonwealth lawyer Tom Howe, QC, says doing so would deteriorate the confidence of current and future cabinets.

The lengthy legal argument, which is yet to be resolved, came after Mr Garrett conceded parts of the scheme were rolled out too quickly.

The great tragedy, he said, was the death of “young boys” who lacked workplace experience.

He said the electrocution of Queenslander Matthew Fuller in 2009, the first death under the program, was a sobering moment.

“I was gutted when that happened,” Mr Garrett said, adding it led to a greater focus on safety.

But that didn’t prevent the scheme going ahead and the subsequent deaths of Rueben Barnes, Mitchell Sweeney and Marcus Wilson.

The scheme was halted on February 19, 2010 amid concerns about shonky operators and unsafe work practices.

Commissioner Ian Hanger, QC, said the government’s desire to quickly roll out the program meant proposed training was scrapped and replaced by “loose supervision”.

“I think that what happened here is it was the newcomers that came into the field who were, for lack of the use of a better word, shonks,” Mr Hanger said.

“Some people … whether they were unscrupulous, careless or cavalier, took the opportunity as it were in a relatively unregulated environment to go about the business in the way they did.”

The Sweeney family will address the inquiry when it resumes in Brisbane on Thursday.

Mr Rudd is expected to take the stand after the Sweeneys.