Deputy Prime Minister Winston Peters has launched a legal battle to find out who leaked details of his superannuation over payment.

Winston Peters' lawyer has said some of the journalists involved in the leak of information about Peters' superannuation overpayments may not have been acting as responsible journalists, but political agents.

The NZ First leader's legal team served court papers last week on nine people including former National Party government ministers, journalists and a government department chief executive over the leak which occurred in the leadup to this year's election.

Peters' lawyers are requesting documents from the parties named in the legal action to try and get to the bottom of where the leak came from, and who was involved.

Warwick Smith/Stuff Former Prime Minister Bill English is one of the nine people to have been served papers.

The first call for Peters' case was heard in front of Justice Anne Hinton on Monday morning at the High Court in Auckland. It was a largely procedural hearing, with all parties represented by lawyers.

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Peter's legal counsel Brian Henry told the court some of the journalists who were leaked the story may have been politically motivated, and not neutral reporters.

Newsroom co-editor Tim Murphy and Newshub journalist Lloyd Burr were both served documents as they knew about the leak before it became public.

Murphy had tweeted in the days before the leak "the mother of all scandals" was about to break.

"The situation is about an illegal act, not dirty politics. When it comes to the journalists, it is our understanding some of the journalists were not 'journalists' but political agents," Henry said.

"...I don't know if [Murphy] was acting as a responsible journalist, or big mouthing around town, or involved in a political set up.

"This was a political set up from woah to go," he said.

Henry said they were considering challenging the pair's journalistic privilege.

Murphy's lawyer Andy Glenie told the court it was not yet clear who Peters planned to take further action against.

"It is not clear which parties are in the gun," he said.

Justice Hinton told Peters' lawyer they will need to file documents with the court detailing exactly what they are alleging against the parties involved.

Ministry of Social Development chief executive Brendan Boyle, National leader Bill English, his former chief of staff Wayne Eagleson, former ministers Paula Bennett, Steven Joyce, and Anne Tolley are also caught up in the legal wrangle.

Former National Party campaign communications manager Clark Hennessy is also named, with the affidavit lodged in the High Court alleging he was the most likely source of the leak.

Justice Hinton set down a hearing for March next year where it will be ruled if the parties will need to disclose the documents.

In a statement on Monday morning, the National Party said: "The National Party people named all continue to refute any suggestion they had any involvement in the leak of this information and will be responding accordingly."

'LEAK WAS MEANT TO DAMAGE REPUTATION'

The affidavit seen by Stuff details how Peters applied for his superannuation in March 2010 in person with his partner, Jan Trotman.

It outlines a timeline of meetings and discussions once an error in the amount paid was discovered.

The affidavit then refers to a "no surprises" briefing given to the then-minister, Tolley, by Boyle.

"The briefing, while required by the National Party government, has to the best of my knowledge no basis in law. The no surprises policy is considered by myself and counsel to be both a breach of the Privacy Act requirements and the duty of care to protect my client's private information held by the MSD."

The verbal briefing was followed up with a written note.

The affidavit then refers to an approach by Newshub's Burr, who "claimed to have a story leaked to him by IRD".

It also refers to Newsroom's Murphy boasting "the mother of all scandals" was about to break, and states former finance minister Steven Joyce was heard at the National Party conference that weekend claiming that a "full load" story was coming out about Peters.

With that knowledge, Peters issued a pre-emptive press statement, the affidavit states.

"It is clear from the media details that prior to my client being forced to issue a media statement to mitigate damage someone had leaked the details of my clients meeting with MSD. The most likely reason for the leak was to damage his reputation in the forthcoming general election."

Prime Minister Jacinda Arden has commented on the legal battle saying it was a "personal matter".