Sir John Key may have got the country through earthquakes and recessions, but the one thing he wishes he could have changed was the flag.

In an interview with the Australian Financial Review, Sir John said his greatest regret from eight years as New Zealand's leader was not being able to change the flag.

He said he wanted to change the flag to something that was uniquely New Zealand; in doing so, he hoped Kiwis could build a more overt sense of national pride.

"This is not the most important issue by a long way for the country, but ultimately I was unsuccessful in changing the New Zealand flag and I have always thought back on that," Sir John said.

He felt the flag referendum didn't fly because the Greens and Labour turned it into a political issue.

"It is not going to change the world and there are many things we did, from the Christchurch earthquakes to economic issues that we dealt with, but that is the one I feel I definitely failed on," he said.

"To be frank, I think I should have just pushed it even harder."

The article saw Sir John touch on his upbringing and how his mother raised him in a low income household.

"My mother was a very determined Jewish matriarchal woman. She always used to say, 'You get out of life what you put into it'."

Newshub.