A dozen current and former senior public servants involved in the unlawful robodebt scheme breached their code of conduct, including former department bosses Kathryn Campbell and Renee Leon.

Sixteen public servants were referred to the public service commissioner for investigation last year, including current employees named in the sealed section of the robodebt royal commission's final report.

On Friday morning, the commission reported "12 current and former public servants and former agency heads have been found to have breached the code on 97 occasions".

Sanctions have been imposed against four current employees who breached the code, including reprimands, fines and demotions, but the commissioner said a number of others who were referred had since retired or resigned and could not be sanctioned.

The commission noted in a number of cases that, had the respondent still been an employee, the recommended sanction may well have been termination due to the seriousness of the breaches.

The robodebt scheme was an automated tool for assessing and recovering Centrelink debts, implemented under the government of Tony Abbott, Malcolm Turnbull and Scott Morrison, before it was ultimately found to be unlawful.

The Australian government lost a lawsuit in 2019 over the legality of the scheme, and settled a class action the next year in which it agreed to pay $1.8 billion in repayments and compensation.

Commissioner names former department heads for breaches

Commissioner Gordon de Brouwer apologised on behalf of the public service for the failures found through the robodebt inquiry.

Among the breaches found were failures to behave honestly and with integrity, failure to act with care and diligence, providing false or misleading information in response to an official request and failure to uphold public service values.

Against former secretary Ms Campbell, the commissioner found 12 breaches, including failure to seek legal advice, failure to sufficiently respond to public criticism and whistleblower complaints, failure to inform the responsible minister and creating a culture that prevented robodebt from being scrutinised.

Mr de Brouwer said Ms Campbell also "caused the resumption of income averaging under the scheme in August 2017 when she knew, or ought to have known, that debts raised pursuant to that process were potentially inaccurate".

Against Ms Leon, who served as secretary from September 2017 to early 2020, Mr de Brouwer found 13 breaches, including misrepresentations of the department's legal position on income averaging, failures to correct or qualify that position and failures to "expeditiously" inform the responsible minister of advice on the lawfulness of the Robodebt scheme.

In a statement, Ms Leon defended her role in the robodebt scandal.

"I am disappointed with the way the Australian Public Service Commission has come to its decision, and I stand by the actions I took to get definitive legal advice and bring the robodebt program to an end," she said.

"Robodebt had already been in operation for two years when I became secretary of human services. When legal doubts were raised, I sought definitive advice from the solicitor-general. I acted as expeditiously as possible to convince a government that was wedded to the robodebt program that it had to be ceased.

"When ministers delayed, I directed it be stopped. Two weeks later, my role as secretary was terminated by a government that did not welcome frank and fearless advice."

Charles Sturt University, where Ms Leon now works as vice-chancellor, said it supported her "courageous and ultimately successful efforts to help end robodebt".

Commission says leadership failures set problematic culture

The commissioner said failures by leadership had direct consequences on those downstream.

"Adverse behaviour in senior leadership is intimidating, creating a culture where employees feel discouraged to provide clear and comprehensive advice to highlight risks or issues," the report said.

"The fact that some leaders, on numerous occasions during the design and delivery of the scheme, failed this standard of care and diligence in connection with APS employment, had a consequential impact on more junior staff who limited their own performance to reflect the workplace leadership practices and culture they observed."

The task force said it took all reasonable steps to ensure it did not exacerbate "the human toll of the Robodebt scheme", including among public servants.

"Being the subject of a code inquiry is confronting and distressing for any public servant. The consequences of an adverse finding on a respondent’s financial position, career development and professional reputation can be significant," the commission said in its report.

Finance Minister Katy Gallagher said the robodebt scheme was one of the worst failures in the history of the public service, and thanked Mr de Brouwer for a "fair" and "robust" inquiry.

"Some former departmental secretaries and public servants made mistakes, showed a lack of care, diligence, integrity, and leadership and they are being held to account for the part they played in the robodebt failure," she said.

"There are many lessons to be learned, and the [Australian Public Service] will continue to work to rebuild the trust of the Australian people to ensure this shameful chapter is never repeated."