The Attorney General has conceded that all Centrelink debts raised using income averaging are unlawful, even those from years before the ‘Robodebt’ issue.

Australia’s attorney general, Christian Porter, has admitted that raising debts through “income averaging” is unlawful, and his admission could open the door to waves of legal claims for refunds from victims saddled with automatically-generated debt notices before 2015.

Mr Porter was interviewed about the matter over the weekend.

He refused to apologise to the thousands of people who have been wrongly accused of owing the government money because there is an ongoing class action by Centrelink ‘robodebt’ recipients.

However, he confirmed that the government’s plans to compensate 460,000 victims a total of $720 million only applies to those targeted after 2015. This is despite the income average method being used for well over 20 years.

The Australian Taxation Office has been using income averaging technology - which looks for debts using ATO annual income data compared against fortnightly pay reported by Centrelink recipients - for decades, but only as a last resort, until 2015.

In 2015, the Coalition government removed human intervention from the program. Mr Porter was asked whether this made it illegal.

“That’s not what made it legally insufficient. It was the fact of the averaging of the data,” he said.

He admitted that the pre-2015 system “was also not a sufficient basis for raising debts, even before the automation”, but ruled out any compensation for unlawful debts raised before 2015.

Experts have called for a judicial review and full audit of all Centrelink debt files.

The Gordon Legal class action on behalf of post-2015 robodebt recipients is headed for mediation next week. The Federal Government says it is yet to finalise its position.

Shadow minister for government services, Bill Shorten, says the methods should be definitively scrapped.

“The government needs to rule out today the people they are refunding, they are not going to try and get again,” he said.

“After all, the government spent $63 million on debt collectors over the last few years, chasing debts they were never the owed, using taxpayer money.”