NZ First leader Winston Peters has claimed he is victim to "filthy politics" and is considering his legal options as three investigations began into how his superannuation details were leaked into the public arena.

Peters is pointing his finger at the National Party as the possible "leak" to the media of the news he had to repay overpayments for his superannuation since 2010, saying it was an attempt to destroy NZ First.

That followed revelations that two ministers - Paula Bennett and Anne Tolley - were briefed on the overpayments by Government department heads under a "no surprises" policy.

National leader Bill English said he did not believe the leak had come from National and was assured by Bennett and Tolley they had not passed on the information.

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Ministerial Services are now looking into the handling of the information by the ministerial offices involved. Both the Ministry of Social Development and Inland Revenue are also now investigating to ensure the leak was not by a public servant.

Peters said he would speak to his lawyer about his options and was determined to get to the bottom of the matter so people could have confidence when dealing with Government departments.

"There's no way I think the fair-minded people of this country are going to put up with this sort of carry-on when it's deceitful, it's duplicitous, it's all the worst elements of dirty politics."

However, he did not say the incident would make it difficult to go into a governing arrangement with National after the election, saying he did not put personal interests about national interests and it would be for the voters to decide.

Peters has also signalled he will complain to Privacy Commissioner John Edwards.

Edwards said he could not comment on the use of the "no surprises" policy in this instance until he had done an investigation - and whether that would happen before the election would depend whether he could access the information and people he would need to talk to.

State Services Commissioner Peter Hughes defended the decision to inform the ministers, saying it was carefully considered and the Solicitor General consulted.

However, English said the Government departments should not have told ministers, given the personal nature of the information.

"Frankly, the ministers would probably have preferred not to be advised about it. There's a question as to whether it was the right judgment by the public service to advise ministers when it involved a senior politician during an election campaign."

He said the ministers had handled it "with integrity".

Bennett said she knew the information would be "explosive" so decided not to share it even with her staff. She denied National had leaked it, saying there would be little benefit in it for National and it was not the kind of behaviour she would engage in.

NZ First candidate Shane Jones has also waded in, saying Peter Hughes' actions in telling Bennett bordered on "a sackable offence".

"I think it's absolutely and utterly reprehensible that the chief executive of the State Services Commission became embroiled in the private superannuation or Inland Revenue issues of a senior politician."

Tolley was first told by MSD chief executive Brendan Boyle on July 31 and got an update from MSD on August 15. Tolley also told the PM's chief of staff, Wayne Eagleson, who has denied telling anyone else in the office, including English.

Labour leader Jacinda Ardern said there was a need to get to the bottom of it to ensure people's privacy was protected by Government departments and whether it had gone beyond that.

She was concerned it was distracting from the campaign and feeding the perception that dirty politics was rife.

The Ministry of Social Development said Brendan Boyle was first advised on June 19 as part of a routine briefing. On July 27 he was advised the matter had been resolved to officials' satisfaction.

Boyle asked the State Services Commission if it should be disclosed to the Minister under the "no surprises" policy and was told to do so. That happened four days later on July 31 at a one-on-one meeting with Tolley. It was followed up with a written note on August 15.

Newshub have reported they got an anonymous tip-off by phone three days later on August 18. Newsroom has also reported details of the repayments, claiming the total Peters paid was $18,000 and the overpayments were detected when Peters' partner Jan Trotman applied for superannuation.

It is not known how much detail the ministers were given, but Peter Hughes said they were given "very limited details".

It remains unclear who was at fault for the overpayments - Peters was on the rate for a single person who was sharing accommodation rather than someone living with a partner.

He has said he took his partner Jan Trotman with him when he applied for super in 2010 but neither MSD nor Peters will release his initial application form or reveal how much he had to repay. Peters said they were unable to work out how the error was made.

Timeline for the Peters super saga:

June 19:

Ministry of Social Development officials tell chief executive Brendan Boyle of an issue with Winston Peters superannuation payments.

Mid-July: Winston Peters says he is contacted by MSD and arranges to repay overpayments.

July 27: Boyle is told the issue is resolved

July 31: Boyle tells Anne Tolley at a one on one meeting. He has consulted State Services Commission head Peter Hughes about "no surprises" policy.

August 1: Hughes tells State Services Minister Paula Bennett. Says "very limited details" given.

August 15: Boyle updates Tolley via a written note.

August 18: Newshub get an anonymous tip about the payments, according to the broadcaster.

August 20: Labour Party campaign launch

August 26: Newshub asks Peters about the super payments.

August 27: National Party campaign launch.

August 27, 7.05 pm: Peters issues statement on the issue after questions from Newshub.