The Deputy Prime Minister insists her party did not leak the fact Winston Peters had been overpaid his Superannuation for seven years.

The Ministry of Social Development and Inland Revenue have begun investigations into whether the information came from any of their staff.

But there's suspicion it was leaked by National MPs, as an attempt to smear Mr Peters.

Paula Bennett told Larry Williams she's sure it didn't come from a government minister.

"The most gossip I've heard was on the TV this morning and a reporter saying that they got an anonymous phone call at some stage. Well, that certainly isn't the way that anyone works around here and it certainly wasn't from us", she said.