Key Points:

The questioning of John Key over his Tranz Rail shares is relevant to the upcoming election with the issue of trust making all parties vulnerable, an Auckland political expert has said.

Associate professor Raymond Miller, head of political studies at the University of Auckland, said while it might not be the primary issue, trust would be important.

"Everyone is vulnerable when an issue like this is run. No one can be completely in control. We've seen Labour has been very vulnerable on this issue and are taking risks by making it one of the themes of the campaign but equally the other political parties are all vulnerable as well," Dr Miller said.

He said the questioning of John Key over his Tranz Rail shares was "fair game" and relevant.

John Key has been accused by the Government of lying about how many Tranz Rail shares he owned while asking questions in Parliament about the rail company.

He said John Key made a "bad stumble" when answering questions by a TVNZ journalist about just how many shares he had in Tranz Rail at the same time as asking questions on the topic in Parliament.

Mr Key said initially said his family owned 25,000-50,000 shares but then corrected himself, saying: "Sometimes 50,000, sometimes 100,000" before saying: "yeah, sorry, it was 100,000 in total".

Dr Miller said: "It was clear that he actually did know because he corrected himself when questioned about how many shares he did have, so that was unfortunate".

He said Mr Key had "done the right thing" by apologising .

"The public are very forgiving of people when they say: OK, I blew it. The problem with Winston is that he has never done that," Dr Miller said.

The topic of trust and Mr Key has already attracted 28 pages of feedback on the Your Views pages of this website with readers about evenly split on their response .

Jane Chalmers from Blockhouse Bay said the issue was not about how many shares he owned but "that he is not upfront. Quite a problem for someone who may be the next Prime Minister of NZ".

Karlos from Auckland Central points the finger at "Aunty Helen" and tells readers: "Just remember, Corngate, Paintergate, Speedergate, Taito Phillip Field and, more recently, Winston Peters".

In a poll running on nzherald.co.nz today, 66 per cent of the first 1300 respondents said they did trust Mr Key.