The police file on the "Teapot Tapes'' says NZ First leader Winston Peters would have been considered as a target for prosecution if charges were laid against the cameraman who recorded the pre-election conversation.
It says Mr Peters' actions repeating details of the recorded conversation meant he would be in the frame - if charges against Bradley Ambrose went ahead.
The recording was made when John Key met Act leader John Banks in a show of pre-election support. It has never been broadcast by media, although Mr Key went to police alleging the recording happened in a ``News of the World''-style operation run by the Herald on Sunday and Mr Ambrose. The claim was denied by both.
After investigating, police said no charges would be laid although they believed Mr Ambrose's actions were unlawful. Mr Key had rejected charging Mr Ambrose after receiving a ``letter of regret'' from the camera operator.
The Herald has seen a section of the police file showing Mr Peters was being considered for criminal investigation - but only if Mr Ambrose was charged. The link to Mr Peters was his pre-election drip-feeding of portions of the tape.
A section of the police file obtained by the Herald stated "there is the matter of Winston Peters quoting from the recorded conversation''.
"There is no doubt he quoted from in albeit very short pieces.
"If the decision is made that Ambrose has committed the offence of unlawfully recording a private conversation then Peters (would) be investigated for disclosing the same.''
Mr Peters, who claimed police sought his phone records, said the Prime Minister's decision not to lay charges had to be considered in light of the police position that it would trigger a criminal investigation against the NZ First leader. He said the scandal would have "exploded into another dimension'' if it had led to a political party leader being prosecuted as a result of a complaint by the Prime Minister during an election.
"It wouldn't just be buying a fight with me, it would be buying a fight with the whole political system.''
The documents seen by the Herald also confirm Mr Eagleson was regularly informed by police. One reference said he would be told the file was being sent from Wellington to Auckland, showing the level of detail on which he was being briefed.
Mr Peters said the frequency of contact was an issue, with the PM's office being briefed more regularly than criminal complainants would normally expect.
He said the investigation should never have taken place. "I thought Ambrose was totally innocent,'' he said. The confusion over the microphone reflected "one man trying to do three jobs'' in an under-funded media. He said he wanted the entire police file released.