ACT Party leader Don Brash says he accepts the release of the cafe conversation between National Party leader John Key and ACT candidate John Banks could be in the public interest.
Mr Key and Mr Banks were recorded without their knowledge while they had a cup of tea during a photo opportunity last Friday.
Two media organisations have a copy of the recording but have not published the details.
Mr Key has complained about the recording to police.
Don Brash told Morning Report he agrees that not releasing the tape suggests Mr Key has something to hide.
However, he says it is not his decision to make.
"Essentially the Prime Minister was hosting that cup of tea and I think it's his decision to release it or not," he says.
He agrees there is public interest in the tape's contents and that the continued secrecy is fuelling speculation about what was said.
National Party president Peter Goodfellow had agreed to an interview with Morning Report on the subject but withdrew on Wednesday morning. Mr Key and Mr Banks had declined to be interviewed.
No overseas plans
It has been suggested that Dr Brash's leadership of ACT was one of the topics discussed, including the possibility Dr Brash could be appointed to a diplomatic post after the election.
However, Dr Brash says Mr Banks has assured him the party is going into the election with him remaining as leader.
He told Morning Report no-one has suggested to him that he should take up an overseas posting.
Dr Brash says he expects to be in Parliament with John Banks after the election and to serve a full three-year term.
He says he has a lot of support within the ACT Party.
Media group urges publication
The Media Freedom Committee, which represents mainstream media, says Mr Key or Mr Banks should release the recording.
Committee secretary Tim Pankhurst says the matter could be put to rest if either man agreed to its release.
He says it would be in their own interest to do so because the issue is starting to dominate the election campaign.
Mr Pankhurst told Morning Report the media has not broken the law as they have not published or broadcast the recording's full contents.