Winston Peters' announcement of his Coalition partner on television just over a year ago, rather than telling the leaders first, was more by accident than design.

On the eve of the anniversary of their swearing in, the New Zealand First leader and Jacinda Ardern have sat down for an interview with Newstalk ZB political editor Barry Soper.

Peters admitted for the first time the announcement was made live on television because he was pushed for time.

"We just thought that we'd go for broke and we'd save the public who are the first ones who are entitled to know.

Ardern says that she didn't mind finding out alongside the rest of the country.

"It's pretty fair, they are the ones who gave us the election outcome. We had a quick conversation afterwards and that's when the deputy Prime Minister said sorry I didn't have the chance to tell you."

The Prime Minister rejects the notion she and Peters are an unlikely pairing, and says the basis of their political relationship is the common ground they share.

Peters saying he's impressed.

"You gotta stand back and be a bit amazed that someone could come out in left field in seven weeks and get themselves in the position and being able to say I'm ready to do this job.

Peters says that Ardern went up in his estimation.

"Not that I ever had any underestimation anyway, as we didn't know each other from a bar of salt."

Ardern denies she had any trepidation about working with Winston Peters.

She says Peters had worked with Labour before, so he was a known quantity.

She was asked whether his reputation of being a bit crusty and tough was a worry.

"I think that's slightly unkind language," she laughed.

The Prime Minister insists that their partnership and that of the Government's rock solid.

"It shouldn't come down to personalities and ego, it should come down to the things that New Zealanders want."

The two leaders says that the coalition will last.

"The important thing isn't that the coalition lasts. but that it lasts being a successful government," Peter says.

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