Deputy Prime Minister and New Zealand First leader Winston Peters has begun new legal action in relation to the leaking of details of his superannuation overpayment, and is seeking $1.8 million in total against five defendants, including the Ministry of Social Development.

He is going after the chief executive of the Ministry of Social Development, Brendan Boyle, State Services Commissioner Peter Hughes, the Attorney-General on behalf of the Ministry of Social Development, Paula Bennett, the former National State Services Minister and former Minister of Social Development Anne Tolley.

Hughes and the Ministry of Social Development are new targets in Peters' legal action.

The timing of Peters' action is extraordinary given that he about to become Acting Prime Minister in the next week or so when Jacinda Ardern takes leave to have her baby.

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Peters is refusing to comment.

A spokesman said: "The minister's view is this a private legal matter which is now lodged before the High Court. He won't discuss matters which are sub judice."

Ardern herself is taking the same line. Her spoksman said: "Mr Peters is taking this action in a private capacity and the Prime Minister won't be commenting on any aspect of the case as it is before the courts."

All targets of Peters'action are entitled to apply to the Cabinet to have their legal fees paid - the Cabinet which Peters will be leading.

Some previous targets in Peters' witch-hunt are not named in this action, namely former National Party leader Sir Bill English, former minister Steven Joyce, former chief of staff Wayne Eagleson and National Party staffer Clark Hennessey.

Peters has targeted journalists Tim Murphy, editor of Newsroom, and Lloyd Burr, a former political reporter at Newshub, in a previous action for discovery of documents but is not pursuing them.

It is understood that papers were lodged today in the High Court in Auckland.

About four weeks before last year's election, Winston Peters revealed he had been overpaid the old-age pension for seven years, but that he had repaid the undisclosed amount as soon as he had found out.

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He pro-actively revealed the overpayment in a press statement because media outlets had been asking questions about it.

Peters first accused IRD of having leaked the information but then turned his sights on Boyle, then political rivals.

Boyle sought the advice of his employer, State Services Commissioner Peter Hughes, as to whether such information should be passed on to minister under the no-surprises policy.

Hughes in turn had consulted the Solicitor-General, Una Jagose, before Tolley and Bennett were told.

Tolley said she had also informed Eagleson, who was chief of the staff to the then Prime Minister Sir Bill English.

In Official Information Act documents obtained by Newsroom into the internal MSD investigation, it transpired that 41 MSD staff had been involved in Peters' case and interviews had been conducted with 12 staff who had full access to information on the case.

National has consistently denied having leaked details.

* An earlier version of this story said Peters was seeking damages of $450,000. He is seeking $450,000 from MSD and Boyle; and $450,000 separately from Bennett, Hughes and Tolley.