Fresh questions are being asked about the involvement of the Prime Minister's office in the planning for a radio show that may have broken electoral laws.

The so called "Prime Minister's hour" ran in the lead up to the election last year.

Police are investigating it after the Electoral Commission found it may have broken laws.

Labour deputy leader Grant Robertson has released emails between John Key's office and the programme's producers that he says show his staff were involved in the editorial layout of the show.

"The Electoral Commission have said that this wasn't an election advertisement because editorial control was held by Radio Live," he says.

"What these emails show is that the Prime Minister's office was involved in what the content of the show would be, who the guests on the show would be and communicating with the Electoral Commission."

It's the commission's ruling that it wasn't an election advertisement because the radio station had editorial control that Mr Robertson wants re-examined.

"We'll be looking at that and seeing if it can be, I'm not sure what information the Electoral Commission had when they made that decision."

He says the PM was heavily involved in the programme, it clearly was an election stunt and he should front up and acknowledge that.

Mr Robertson plans to take the emails to the Electoral Commission today.