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The cameraman behind a controversial recording of Prime Minister John Key and Act's John Banks will be "invited" in for a police interview.

Freelance cameraman Bradley Ambrose is at the centre of the police investigation after Key alleged the recording - during a pre-election chat between the two politicians on November 12 - was obtained illegally.

The complaint is being handled by East Auckland Area CIB head Detective Senior Sergeant Kevin Hooper but a spokeswoman said: "A significant amount of work had already been completed in Wellington before the file was received."

Hooper said many people the police wanted to talk to were away but they would continue to try to contact them. "Once that part of the investigation is complete, detectives will invite Mr Ambrose for an interview."

Ambrose's lawyer, Ron Mansfield, said his client would co-operate fully with the inquiry. "We're trying to get it concluded with as soon as possible so he can get back to work."