Mr Key admitted in Parliament yesterday he had chosen the interview subjects for the show, but said he did not know his staff were involved in changing the show's brief or had drafted the request for RadioLive to get an opinion from the Electoral Commission before it aired.
The Electoral Commission referred the Prime Minister's Hour programme to police last week, saying RadioLive aired an election programme in breach of the Broadcasting Act. However, it was decided the programme was not an election advertisement because Mr Key was under the editorial control of RadioLive.
Mr Robertson said emails from Mr Key's office showed he was heavily involved in the content of the programme and knew it could possibly breach electoral rules but believed the blame would fall on RadioLive.
He would refer the emails to the Electoral Commission to see if it had been aware of them when it decided that Mr Key was acting under the editorial control of RadioLive.
The emails show RadioLive did send instructions regarding the show to the Prime Minister, saying his office should provide him with lines to use if he was asked about voting. RadioLive also said its own lawyer was "totally comfortable" unless the Prime Minister "starts telling people how to vote".
Mr Key also had leeway over the questions he asked: RadioLive sent "draft" questions only and asked one guest what he wanted to talk about.