Acting Prime Minister Winston Peters says the leak about his pension overpayment continues to hurt his reputation with many people still wrongly believing he was involved in a "shady deal".
Mr Peters has been giving evidence in the High Court at Auckland on the first day of his privacy case against former National ministers, top civil servants, and a government department.
The NZ First leader argues that his privacy was breached in 2017 when officials notified then-National ministers Paula Bennett and Anne Tolley that the MP had been overpaid nearly $18,000 in superannuation over seven years and had paid it back.
"It is still brought up by my detractors as a slur on my character to this very day," Mr Peters told the court.
Mr Peters said the overpayment was due to an error by ministry staff who processed a form which was incomplete.
He had filled out his pension application at an MSD office in 2010 alongside his long-time partner Jan Trotman who he introduced as such, Mr Peters said.
The NZ First leader told the court he had declared on the form that he was living separately from his wife, but he was not living alone.
One question on the form was not filled in and yet it was still processed by the ministry, he said.
"Such a mistake is hardly a matter of ministerial responsibility and the officials knew this."
Mr Peters said he found it "repugnant" that his private details were given to his political opponents, despite them having no ministerial responsibility, a month out from a general election.
In his opening address, Mr Peters' lawyer Brian Henry said the case was about damage to his client's reputation.
"This is a genuine clerical mistake, nothing more. The public servant processed an incomplete form, nothing more," he said.
Mr Henry said the staff member could have simply asked Mr Peters to complete the question, but did not.
"Proper processes are designed to be followed. Their purpose is to avoid mistakes. The failure of the MSD to apply its own proper process caused the mistake."
Mr Henry signalled that it was "disputed" whether Ms Trotman was present at the initial MSD interview as both Mr Peters and his partner claim.
While Prime Minister Jacinda Ardern is in Thailand for the East Asia Summit, Mr Peters is acting in her role. However, due to Mr Peters' appearance in court, Labour deputy Kelvin Davis chaired Monday's Cabinet meeting.