Former Liberal minister Christian Porter has told the Robodebt royal commission he takes responsibility for the failed scheme.
As social services minister between 2015 and 2017, Mr Porter, and then-minister for human services Alan Tudge, oversaw the Centrelink welfare debt recovery scheme's implementation.
The commission has previously heard his department had received internal legal advice in 2014 and 2017 that showed the scheme was unlawful.
Officials never took action or escalated the advice and the scheme continued until 2019, wrongly accusing hundreds of thousands of welfare recipients of owing money to the government.
Mr Porter said he never saw legal advice during his time as minister and agreed with senior counsel assisting Justin Greggery KC that department officials had a "duty" to bring it to his attention.
"I was unaware of all the comings and goings of this issue," he told the commission in Brisbane.
The commission heard Mr Porter met with Department of Human Services (DHS) officials and asked whether there was "sound legislation underpinning … the system as it was operating".
"I firmly had in my mind that I put this question to people and that they'd responded affirmatively," he said.
"I can't recall who … but a departmental person assured me … I can't recall if it was DHS or DSS but someone did. It happened and we moved on."
Commissioner Catherine Holmes said: "You see, Mr Porter, everyone says it [Robodebt's failures] was really someone else's doing and it's a bit hard to get to the bottom of whose doing it was."
"Do you take any responsibility for this?" she asked.
"I do. And I look back on this and I see myself through the correspondence getting quite close at points to taking the next step of inquiry and I didn't do that," he replied.
"I wish now that I had."
Talking points 'inaccurate' and 'untrue'
Mr Porter also admitted he gave "inaccurate" and "untrue" information to the media while defending the scheme after Robodebt recipients came forward in late 2016 and early 2017.
The commission heard department officials gave Mr Porter a list of talking points for media interviews.
They included: "We are confident in the online compliance system" and "80 per cent of the instances of compliance letters going out, there has been a debt raised for the Commonwealth and … has been an overpayment."
Commissioner Catherine Holmes said: "Was that in your talking points? Because it wasn't, of course, true."
"There were lots of things in those talking points that through this [royal commission] process and information from my lawyers provided me from this process, I now understand were inaccurate or untrue," Mr Porter said.
"I was frustrated because I'd gone out and undertaken earlier media based on what were talking points and oral conversations with DHS people or relayed to me … the level of confidence they had [in the scheme] was extraordinarily high.
"And the early media that I did was relaying those talking points and the confidence levels.
"I placed enormous reliance on the … figure that was in those talking points which was about the percentage of complaints.
"I felt that I'd been disserved in terms of the information that I'd been given to go out and do large national media on the issue."
Mr Porter said he became increasingly frustrated with a lack of clarity from bureaucrats about how the scheme was operating.
"As we went further into … interrogating what was actually occurring, it seemed to my office and I that the processes hadn't been very well designed," Mr Porter said.
Mr Porter said he relied on knowledge that the program "would have been scrutinised as to the issue of whether it required legislative change or not" and had gone through a "rigorous" cabinet process.
He added that it was "fairly accurate to say that I did not understand precisely how a debt was ultimately being issued and completed" but he thought there were "obviously clunky" and "easily fixable" elements of the scheme.
'I recall the prime minister being concerned'
Earlier, former minister Alan Tudge wrapped up his testimony after a marathon hearing on Wednesday.
Mr Tudge said he was aware "income averaging" could cause "inaccurate" welfare debts but he believed the method had been used for decades and so it did not cross his mind "that it could possibly be unlawful".
He revealed he met with then-prime minister Malcolm Turnbull, Mr Porter and some department officials when media criticism of the scheme escalated in early 2017.
"I recall the prime minister being concerned about what happened, why did this system go awry?" Mr Tudge said.
"I remember him reflecting on the fact that there needs to be more rigorous testing before a system is rolled out."
Mr Greggery asked: "Did you present a rosy picture, or did you tell him [the prime minister] all of the real concerns you had, which obviously didn't include lawfulness and accuracy?"
"I don't think we went through in detail how the overall system works, my recollection is we very much went into what went wrong with the implementation," Mr Tudge replied.
Mr Tudge repeatedly said only Mr Porter or Mr Turnbull had the authority to stop the scheme.
Mr Greggery put to Mr Tudge that "it would have been prudent" to have obtained legal advice on the "contested questions of accuracy and lawfulness" circulating in the media at the time.
"Definitely," Mr Tudge agreed.
Mr Turnbull has not been called to appear at the commission. The third block of public hearings concludes on Friday.
