Police asked questions about Mike Sabin six months ago

Police were asking questions about former Northland MP Mike Sabin back in August last year.

The revelation comes as questions continue to dog John Key about when he found out about Mr Sabin’s troubles. Source: 1 NEWS

Sources have confirmed this to ONE News as questions continue to dog Prime Minister John Key about exactly when he found out about Mr Sabin's troubles.

National MPs met today at the first caucus of 2015, minus one, Mr Sabin, after his sudden resignation last Friday for family reasons.

MPs and party chiefs questioned by reporters are sticking to the Prime Minister's line that he first knew in December.

But ONE News has tonight confirmed that in early August police started looking into allegations against Mr Sabin. Two months later, on October 22, he was appointed chair of law and order select committee.

"Mike Sabin was a chair of the law and order select committee and...if there was a police investigation then there was a potential conflict of interest," Labour leader Andrew Little says.

ONE News started making inquiries to government agencies and Mr Sabin on November 25. December 1 is now when Mr Key says he first heard Mr Sabin had family issues. Then, last Friday, January 30, Mr Sabin resigned.

"He is dealing with a family matter. Yep, he probably should have come and told us and that would have been useful. But he didn't and we didn't know about it," Mr Key told reporters today.

This evening, a spokesperson for Mr Key confirmed his chief of staff probably knew about the Sabin matter nearly at least a week before he told the Prime Minister.

"It just goes against every bit of information that I have received and that I have seen that senior ministers, at least the Prime Minister and the Minister of Police, would not have known about it," Mr Little said.

ONE News political reporter Katie Bradford says police are not expected to inform the Prime Minister of every investigation. "That is of course an operational matter. But it is the duty of Mike Sabin, under what's known as the 'no surprises agreement' to tell his boss just what's going on," Bradford said.

One MP who confirms he did get the early heads up is Rodney MP Mark Mitchell, who admits he and Mr Sabin speak daily. "Yeah, he was pretty candid. He confided in me, yeah, as a mate would do," Mr Mitchell told reporters.