Prime Minister John Key has admitted he keeps a dirt file on Labour MPs in his top drawer.
Mr Key insists the National Party is not behind the revelations about Auckland Mayor Len Brown's extra-marital affair.
But the Prime Minister says he receives a lot of scandalous information.
"I've had plenty of people who've rung me up with information about Labour MPs," he said.
"And I've done the same thing to every person that's rung me. I've written it down, put it in my top drawer and kept it to myself. I'm just not interested in engaging in it."
Mr Key quipped that if he writes a book one day, people will find it "quite fascinating".