This has, if anything, lent further weight to ongoing calls for a royal commission into the scandal which affected more than 370,000 people. Many believe the real intention in settling the class action bought by Gordon Legal was to avoid an almost certainly highly embarrassing court case. The PM might have even been called upon to testify.

As the social services minister during robodebt's conception in 2015, and as the treasurer and then Prime Minister for much of the time it was in operation, Mr Morrison has more skin in this game than any other former or current cabinet minister. And that is precisely why the government he leads should not be allowed to buy its way out of trouble.

As Bill Shorten, the shadow social security minister, has noted a thorough and independent investigation - preferably in the form of a royal commission - is now more important than ever.

Robodebt, as the $1.2 billion cost of the clean-up indicates, is among the most catastrophic, politically driven, bureaucratic bungles in Australia's history. Taxpayers who are footing the bill for what effectively amounts to a let-off pass for select senior cabinet ministers have a right to know what went wrong, who was to blame, how they have been - or are going to be - dealt with, and what can be done to make sure the dubious practice of "income averaging" is not used to unleash real debts ever again.

While, in the wake of inquiries into sexual abuse, banking, aged care, and the bushfires, many are probably suffering "royal commission fatigue", no other instrument stands a chance of getting to the bottom of these questions.

Whatever costs are incurred during this process surely won't come close to the $721 million in refunds, $112 million in compensation, and $398 million in cancelled debts the Treasurer now has to sign off on.

Australians need to know, at the very least, how an initiative lauded as likely to save $1.7 billion over five years, against an outlay of just $240.4 million in May 2015, has blown such a hole in an already very battered federal budget.

Part of that answer will probably be found within the ideological settings of the Abbott government which took office in 2013. Core assumptions appear to have included the view that many of those who were on welfare were cheating the system and that the APS was suffering from a surfeit of staff.

An obvious way to kill two birds with one stone was to use data-processing algorithms based on the principle of income averaging to estimate debts and then generate letters of demand that, untouched by human hands, were whisked away to their surprised recipients by Australia Post.

While income averaging had, as this government has repeatedly told us, been used previously, it had only served to identify potential debts, which were then reviewed by appropriately trained and authorised staff.

The result was a great deal of stress and anxiety for hundreds of thousands of people who suddenly found themselves being treated as welfare cheats and potential criminals. This is believed to have contributed to an unknown number of suicides over a period of four years. Arguably the worst aspect of the whole affair is that, although it had become quite obvious the system was flawed by December 2016, the government doubled down, apparently only terminating "sole reliance on income averaging" in late 2019.

Even now, after having agreed to what is believed to be a record payout, it refuses to admit to any legal liability as a condition of the settlement. It's just not good enough.