"One factor taken into account is a letter of regret from Mr Ambrose which has been sent to the Prime Minister and Mr Banks. They have both indicated acceptance of this statement."
Mr Ambrose's lawyer Ron Mansfield said his client maintains that he never recorded the conversation on purpose and has not done anything illegal.
"The team of lawyers assisting Mr Ambrose were confident no offence was committed or could be committed in the circumstances, and this has been clearly conveyed to the police."
He declined to comment on the timing of the complaint to police by Mr Key and whether that was done to prevent other media from publishing the contents of the conversation.
"It certainly didn't warrant a prosecution, that would just be a further waste of taxpayer funds."
In a letter to the Prime Minister, Mr Ambrose said the recording of the incident was a mistake and he regrets passing the recording on to other media.
"This whole event has been blown out of proportion by a number of people and I would like to put it behind me.
"I just want to get back to work and not be known as someone alleged to have dubious ethics. This has been hard on me and my family."
He said he would have deleted the tape, had he known the effect that it would have.
"I have become much wiser and more protective of my reputation as a result of this event and what has transpired."
Police have for months been considering whether to proceed with charges against Mr Ambrose who recorded a conversation between Prime Minister John Key and Act Party Epsom candidate John Banks at central Auckland's Urban Cafe in the final weeks of last year's election campaign.
Mr Ambrose says he recorded the conversation inadvertently at the staged event to which media were invited to witness and report on Mr Key's endorsement of Mr Banks.
However, Mr Key laid a complaint, saying the conversation was private and Mr Ambrose's recording of it was illegal.
The tape, in which Mr Key made comments about NZ First's voters and discussed the future leadership of the Act Party, dominated media coverage in the final weeks of the election campaign.
It also provided a boost to NZ First leader Winston Peters, who leaked what he alleged were the contents of the conversation, to gain traction in the media.
Mr Key made his complaint to the police shortly after the incident but Mr Ambrose then went to the High Court asking for the conversation to be declared public. However Justice Helen Winkelmann was unable to make a judgment on the matter.
Attorney-general Chris Finlayson is seeking nearly $14,000 in court costs from Mr Ambrose over that High Court action in a matter that remains before the courts.
