Former social services minister Christian Porter has conceded departmental legal advice casting doubt on the legality of the robodebt scheme should have been given to him.
Mr Porter, who served in the role between 2015 and 2017, appeared before the royal commission into the robodebt scheme on Thursday.
The former minister said he was never provided with internal advice held by the Department of Social Services, which was created in 2014, that raised legal concerns with robodebt.
The robodebt scheme began in 2015 but continued well after significant concerns were raised about its legality until it was found to be unlawful in 2019.
Mr Porter said he never received the legal advice during his time as minister but admitted he should have been provided with it.
He said if there were issues with the legality of the robodebt scheme, he expected he would have been told by the department.
"I didn't turn my mind to what particular issues might arise in the legislative underpinnings, but I knew that you would have to be assured of those underpinnings, at the time, that was something that would have been tested," he said.
The robodebt scheme recovered more than $750 million from more than 380,000 people. Several people took their lives while being pursued for false debts.
The unlawful scheme involved using annual tax office data to calculate fortnightly earnings and automatically issue welfare debt notices.
Mr Porter said he was frustrated with department staff when trying to get information about robodebt.
"As we went further into the process of interrogating what was actually occurring, it seemed to my office and I that the processes hadn't been very well designed," he said.
"They were inefficient, there were issues and problems with them, many of them are common sense things."
The former social services minister said he first learnt of the robodebt scheme in April 2016 from a ministerial submission.
He also said talking points provided to him which he used in media interviews during that time avoided the question of whether income averaging was used as a way to calculate debt.
Earlier, the commission heard from former human services minister Alan Tudge, who said he had not considered whether there was legal authority for robodebt notices to be sent out.
"My mind was not acting as a lawyer. It was acting as an implementer of the policy," he told the commission.
"I'd understood that (income averaging) had always been used for decades and so it had not crossed my mind that it could possibly be unlawful."
However, royal commissioner Catherine Holmes said the minister's approach to the scheme was indifferent to the mounting criticisms, particularly on the legalities of the program.
"It seems a fairly blithe approach for a minister, particularly in the light of controversy, to assume that because it's happened before for a long time it must be fine," she said.
Mr Tudge denied he had taken such an approach.
"My rationale was multifaceted in terms of why it had not crossed my mind that it would be unlawful," he said.
"One of the pieces of evidence ... was that it had been through a cabinet process, which I know is rigorous."
The commission will continue hearings on Friday.
