Police will execute a search warrant on the offices of the Herald on Sunday tomorrow.
The search is part of their investigation into Prime Minister John Key's claim he was deliberately bugged.
A recording was made when Key met Act candidate John Banks at an arranged media event at a cafe in Auckland's Newmarket.
Key rejected freelance cameraman Bradley Ambrose's explanation that the recording was an accident and lodged a police complaint.
A fresh poll supports Key's decision to refuse permission to publish, with 44 per cent of people backing his stance. Thirty-three per cent of the 1200 people polled thought he should grant publication.
National Party insider Matthew Hooton said the public reaction showed the Herald on Sunday had made the right decision to keep the contents of the recording private without the permission of Banks or Key.
"The judgment was probably right. The Herald on Sunday did in fact decide the Prime Minister's right to privacy outweighed the importance of what was on the tape."
The Key Research poll, conducted for the Herald on Sunday, also showed the National Party had a commanding lead over other parties - enough to govern alone.
The poll was taken over four days and found National had 55.6 per cent support among those polled, more than double the 26.2 per cent polled by the Labour Party.
The Green Party was next on 11.3 per cent, followed by New Zealand First on 3.6 per cent.
The Act Party is wallowing on 0.5 per cent and its hopes hang on the Epsom seat deal, which was the subject of the "tea party" between Banks and Key.
On Tuesday, the focus will shift to a High Court ruling sought by Ambrose on whether the conversation was private.
Ambrose said yesterday that he needed to get a court ruling because his work prospects were being affected. "It's a very uncomfortable position to be in. I like to be behind the camera. The thing I'm trying not to think about is whether I will have enough work to survive."
Voters casting their ballots early in Epsom yesterday were scathing about the deal between Act and National. Votes for National outnumbered those for Act by almost three to one. Remuera's Angela Hill voted for the Greens and Paul Goldsmith. "I held my nose and voted for the National candidate as I don't want to see John Banks [win]." But Banks said the "horrifying prospect" of Winston Peters in Parliament had led to increased pledges of support. Peters repeated his attack on Key for "contemptible and discouraging" comments he said the PM had made.
THE NEWSPAPER'S VIEW
The Herald on Sunday did not "bug" the Prime Minister. We did not know his conversation with John Banks had been recorded until a freelancer gave it to us afterwards. We assessed the tape as having a public interest and asked for the politicians' permission to print. They said no, so we didn't.
It is what we do every week with a mountain of information handed to the paper - is it interesting, is it legally and ethically permissible to print?
That's how the media should operate in a free society.
- additional reporting Cherie Howie