Updated 2.48pm: Winston Peters says it's not good enough for the Prime Minister to remain silent about the personal issues that saw Northland MP Mike Sabin suddenly resign last Friday.

The New Zealand First MP's gearing up for an attack when Parliament resumes in a fortnight, which he says will be like a corpse on a desert floor.

"The Serengeti Plains, when somebody goes down all the vultures are out.

"We're looking straight at the Prime Minister. We want to know what the Prime Minister knew and why didn't he act on it."

Peters thinks Key knew of issues well before Sabin's resignation.

"I think he knew a long, long time ago of concerns that he should, as a Prime Minister, have made a decision on and he's told us nothing.

"Worse than that, he's sought to say there's nothing afoot that I should be concerned about."

Little joins chorus

Andrew Little says he finds it hard to believe the Prime Minister didn't know that his Northland MP Mike Sabin was under investigation before late last year, as he claims.

The Labour leader says it seems everyone else knew.

Mr Little says if he was Prime Minister he would have stood Mr Sabin down from chairing the law and order select committee.

"If I became aware that a member of my caucus was under investigation then that member would be stood aside from any responsibilities that would pose a conflict of interest."