Prime Minister Tony Abbott backs the suspension of rules governing cabinet confidentiality which has allowed Kevin Rudd to give evidence to a royal commission into Labor's bungled home insulation scheme.
It would help uncover the issues that led to the deaths of four workers, he said.
Mr Rudd on Thursday began giving evidence after the commonwealth dropped its objections to the use of heavily redacted portions of cabinet documents.
Mr Abbott said it was important to get to the bottom of what happened under the Rudd-government scheme.
"Let's face it, this is the most disastrous domestic program that the commonwealth government has ever been responsible for," he told Sky News.
"We've got to learn the lessons, and frankly, if Mr Rudd can speak freely ... that surely helps the royal commission do its work."
Mr Abbott said he was not concerned the decision to allow access to the confidential documents set a precedent that could come back to haunt him.
"I'm confident that we won't run a roof-bats style disaster and, frankly, if we ever do, it ought to be investigated."
Mr Rudd had refused to swear an oath about his evidence to the commission, arguing it shouldn't be censored under cabinet confidentiality rules.
His lawyer argued the former prime minister would only be able to give full and frank testimony if he could refer to what happened in the cabinet room.
The commonwealth initially contested Mr Rudd's bid to give uninhibited evidence, saying it would erode the confidence of present and future cabinets.
But its position changed on Thursday.
"The commonwealth now supports public ventilation of the redacted portions of Mr Rudd's statement," its lawyer Tom Howe told the inquiry.