Winston Peters told the Auckland High Court on Monday he is a victim of a "slanderous slur" and his personal reputation has been damaged.
The Acting Prime Minister is taking legal action against a cast of powerful political figures over the leak of his superannuation overpayments before the last election, including National's deputy leader Paula Bennett and State Services Commissioner Peter Hughes.
Peters is laying out his case that his privacy was breached and therefore his reputation damaged after Newshub and Newsroom were alerted to the overpayments.
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Peters has suggested the leak to the media was politically motivated, and it "most likely benefited the National Party", which he says was attempting to eliminate New Zealand First and take back the Northland seat Peters held going into the 2017 election.
He says in the political maelstrom of media coverage that followed, "my reputation was being trashed... the heated debate on social media left many in the public thinking I was involved in a shady deal".
After applying for superannuation in April 2010, Peters was paid at the higher rate given to singles rather than the lower rate given to pensioners in relationships. Peters lives with his long-term partner, Jan Trotman.
Peters says this was an administrative error by the Ministry of Social Development (MSD), and his partner was with him when he applied for the pension, introducing her as his partner to the caseworker and other staff at the MSD office.
It was when Trotman applied for superannuation in June 2017 the overpayment was identified. Once alerted, Peters made a repayment to the MSD of nearly $18,000.
Then Minister of Social Development Anne Tolley and Minister of State Services Paula Bennett were alerted to the overpayments under the ministerial 'no surprises' policy, which requires public servants to alert their ministers of matters of significance within their portfolio when they may be controversial or become subject of public debate.
Peters says his superannuation is a private matter and should not have been raised with ministers.
"Jan and I value our privacy and do not discuss our private matters with others," Peters told the court.
"The ministers had no right to know, and had they not been told we wouldn't be here today."
Peters says the overpayment was not controversial as it was an operational mistake.
"'No surprises' was never intended to circumvent the rights of the average New Zealander and their expectation of privacy," he said, adding it's not designed for "wholesale gossip and trivia".
He is seeking damages of $450,000 in total.
The trial is set down for three weeks at the Auckland High Court. Peters is being cross-examined by Barrister Bruce Gray, QC, who is representing the former ministers.