Winston Peters accuses National of 'filth and dirt'

Winston Peters is on the warpath over who leaked details of his pension over-payments.

The New Zealand First leader says he's the victim of a privacy breach, claiming it's dirty politics orchestrated by the National government - and he'll "lodge a serious action" when his lawyer returns from an overseas holiday today.

And it's been revealed two senior government ministers knew about it, and so did the Prime Minister's office.

Mr Peters got off his campaign bus 'The Straight Talk express' on Tuesday - and took aim straight at National.

"This is just a cover-up, a camouflage, for illegal, illicit, dirty underhand politics," he says.

He claims National leaked details of his pension over-payments.

"This is humbug. It's tawdry. It's dirty. It's filthy, and they should not succeed on that", Mr Peters said.

For up to seven years, Mr Peters' pension was paid at the wrong rate. He was informed of the pension overpayments by Ministry of Social Development (MSD) on July 15.

Mr Peters paid it back almost immediately and though the matter was over.

But the information was passed on to National Party ministers, and even the Prime Minister's office.

On July 31, MSD told minister Anne Tolley about it, under the so-called 'no surprises policy'.

And once Mr Peters had paid the money back, MSD updated Minister Tolley on August 15.

Just three days later, Newshub was informed by an anonymous caller. Mr Peters suspects it was a National Party insider.

"They have breached my privacy," Mr Peters says.

"What I do know is that there's a whole lot of filth and dirt going on here."

But it wasn't just Ms Tolley who knew. The State Services Commissioner told minister Paula Bennett, and it eventually made it to the Prime Minister's chief of staff Wayne Eagleson.

He claims Mr English was never told.

Mr English is vehemently denying the leaks came from his party or his government and questions why ministers were told in the first place.

"It would have been better if public service had not advised ministers," he says.

Mr Peters has raised Paula Bennett's questionable track record on privacy. In 2009, she released payment details of two beneficiaries who criticised the Government - and last year, her office was accused of smearing the chairman of a marae which was housing the homeless.

Mr Peters claims the leaks go all the way to the Prime Minister.

"You've got a political party that's been deeply exposed now. That's all the way to the Prime Minister. Don't tell me Paula Bennett knew and the Prime Minister didn't know," Mr Peters said.

"It's underhand, and it's dirty politics. It's probably, in my view, illegal. Utterly, utterly wrong and apparently they knew even before I knew."

However Ms Bennett says Mr Peters' pension scandal is nothing to do with her.

"So, do we think someone from the Beehive put on a different voice and rung an anonymous tip off to the media? I mean it's just ridiculous," Ms Bennett told Newshub's Emma Jolliff.

"I don't actually go around the back scuffling around doing leaks. I actually, if I've got something to say, I say it directly and up front and kind of bluntly. "

"I hold confidential information. I do that with respect, and I have not leaked."

Internal investigations have been launched at both MSD and the State Services Commission to find the source of the leak, and Mr Peters is on the hunt too.

"I'll find out. I'll find out every last thing. But I will not rely on the State Services commission doing a snow job in-house on me."

The pressure is swinging away from Mr Peters and his pension problem, and onto who's to blame for breaching his privacy.