One of the problems was that even those who supported a change could not agree on a replacement. Mr Key said his own support for changing the flag had strengthened over time. "The Rugby World Cup for me really cemented the view we should change to the silver fern."
He did not believe his wish to change the flag to remove the Union Jack was contrary to his monarchist leanings.
"I don't see how they're related. Some would say it has the Union Jack on it, but there are Commonwealth countries with the Queen as head of state where they don't have the Union Jack on the flag."
Asked if he would like to beat Australia to changing the flag, he said he did not know if they were even considering it. "Whoever headed towards changing the flag, I think it would be controversial but a potentially winnable argument."
Asked whether knowing the royals on a personal level had entrenched his monarchist views, he said he had "an enormous respect" for them.
"It's given an opportunity to see how remarkable they are. They're in fantastic shape, they work extremely hard and they're very knowledgeable."
He said there was a succession line "of immensely able people".
"On one level, that's always going to be a factor in my view. But even prior to that I was always quite strongly of the view that the monarch should remain."
But he did not expect the issue to bubble up in New Zealand soon, not least because of the popularity of the younger royals such as Prince William and his new family. To help persuade the rest of New Zealand, he has invited Prince William and Catherine, the Duchess of Cambridge, to visit with Prince George.
