He continued to decline to answer questions on the details of the tape, even as Winston Peters claimed that the pair undermined Act leader Don Brash.
With only eight days left until election day, the teapot tape has overshadowed the parties' campaigns and has kept the spotlight firmly on Mr Key, Mr Banks and their parties.
Dr Brash has said he takes Mr Banks at his word that nothing embarrassing was said on the tape, but the Herald understands Mr Banks has told some in the party that his comments about Dr Brash may be negative.
The cup of tea that was supposed to be a lifeline to Act has now left the party at the mercy of how the Epsom electorate sees the tape and the comments. If Act does not win Epsom, it will not return to Parliament unless it wins 5 per cent of the party vote.
New Zealand First is rising in the polls and leader Winston Peters continued to use the situation to his political advantage, drip-feeding what he claims are details of the conversation to an Invercargill audience yesterday.
He claimed Mr Banks described Dr Brash as a "strange fellow" and that Mr Key told Mr Banks that Catherine Isaac - third on the Act Party list - should be the party leader.
"Here is the leader of the National Party telling Mr Banks, on whose coat-tails they hope to get back into Parliament, who the new leader of the Act Party should be," Mr Peters said.
He claimed Mr Key insulted elderly people by saying NZ First's "constituents are dying - not voters, not people ... a description John Key uses for hundreds and thousands of New Zealanders who happen to be older".
Mr Peters said the comments showed Mr Key's real character, judgment and credibility.
Mr Key, who was campaigning in Whangarei yesterday, continued to insist there was no interest in the matter except from the media, which should focus on "issues that matter".
He did not walk out in the face of media questions, but he did not answer questions about the tape's contents because it was a police matter.
Mr Key said questions about Dr Brash were a matter for Act, though he said he was happy to work witheither Dr Brash or Mr Banks, and the leadership was a matter for the Act caucus.
The Prime Minister said that he was taking a principled stance, and to consent to the release of the tape would lead to "bad outcomes".
He stood by his comments comparing the recording of the conversation to News of the World tactics, and when asked to respond to suicide victims' families who found his comments offensive, he said: "I feel very strongly about the principle involved.
"[The media] have to have ethics in the way [they] operate in this country and I believe that wasn't on display last Friday."
Radio NZ head of news Don Rood said the broadcaster would protect its sources if police tried to take material.
TV3 director of news Mark Jennings said police viewed the channel's footage of the cup of tea event yesterday, but did not ask for the tape. If they did, said Mr Jennings,"we'd have to think about that".
Mana's Waiariki candidate, Annette Sykes, accused Mr Key of sending in "his heavies" to get rid of any damaging evidence so he could win the election.
"First it was Tuhoe. Now it is the media," she said after hearing of police warrants to search media organisations.