Renee Leon, a former human services department secretary who is now vice-chancellor of Charles Sturt University, appeared before the commission on Tuesday. She became secretary in October 2017, two years into the scheme’s operation.

Professor Leon said the briefing given upon her appointment did not raise any issues with the scheme and she was shocked when she received advice from the solicitor-general that the program was unlawful.

Because it was already established when she took the position, Prof Leon expected any problems had been properly examined before it was implemented.

When the program was discovered to be unlawful, Prof Leon advised Robert that the department should apologise to customers, admit the error and inform the public of steps to correct it.

She remembered Robert replied: “We absolutely will not be doing that. We will double down.”

Prof Leon said some ministers suggested ending the robodebt program while not repaying debts or telling anyone unless people appealed, but she felt this was inconsistent with legal obligations.

Asked what could have led to the scheme continuing for so long, Prof Leon said it was possible senior officers asked themselves the wrong questions about its lawfulness.

But she also raised the possibility people could have doubted the legality but were reluctant to withdraw such a popular proposal that had promised to raise billions of dollars.

“I hope that’s not the case, because the public service ought to have some red lines and lawfulness is one of them,” she said.

Prof Leon said, in her experience, former coalition ministers would stop speaking to secretaries and refuse to deal with them if they presented “unhelpful” advice, whereas officers “responsive” to their policy agenda would be “rewarded”.

“It wasn’t popular to give advice to the (former) government that what they were trying to do was wrong,” she said.

Prof Leon said the rewards included promotions to high-profile government departmental roles.

She believed her determination to provide “frank and fearless” advice to former coalition government ministers contributed to her employment being terminated in 2019.

Former Liberal MP Michael Keenan, human services minister while Prof Leon was secretary, told the commission he trusted his department to provide him with the necessary legal advice.

He said he didn’t think he could access any advice given to cabinet about the proposal before he became a minister.

Commissioner Catherine Holmes said had Keenan looked at the advice, he would have seen it didn’t include a legal opinion about income averaging used to calculate the debts.

Keenan said he did not give any weight to media reports throughout 2018 raising problems with the scheme because he trusted his department.

“I had very firm views about the ability of my department to advise me correctly,” he said.

“I had great faith in their ability to do that and that was the basis on which I formed my views about the legality of the program.”

He was also unaware debt collectors told robodebt victims they faced interest charges or travel bans if they did not pay up.

-with AAP