Deputy Prime Minister Winston Peters says he knows who leaked private information about him but won't reveal who it is.
Peters is going to appeal the High Court decision over the leak of his pension details.
He says he is going back to court on behalf of all people who have had their privacy breached.
"Its not relevant to this case, it's just a sad situation of being at a court case where people were there that knew that that was what they were hearing, not true," he told Morning Report.
"We did not know who the person who leaked the information was until the case was over."
He said the person's identity was not the nub of the case, the nub was the misapplication of the law.
"It's an appeal, every part of this case was found in my favour expect one. It said I had to prove who the leaker was," Peters said.
He later said: "The law on this matter enables you to make an appeal on how the law was applied. It does not allow you to appeal the details of the construct of the original trial.
"It's got no relevance in this situation other than to say we, and others, know who the leak is."
He said someone from the media had told him who the leaker was.
"I'm sworn to keep that person's confidentiality."
Peters says he is paying for the legal action himself, as he did before.