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Labour leader Jacinda Ardern and deputy Kelvin Davis during a media conference revealing their party's new campaign slogan on Friday.

Labour leader Jacinda Ardern has dodged questions about whether she'll be with the party in 2020.

Ardern and Labour deputy leader Kelvin Davis appeared on The Nation on Saturday morning when host Lisa Owen asked if Ardern could guarantee she would still be around in three years' time, regardless of the election outcome.

Ardern said she wasn't going to concede that Labour might lose and that talking about her being the next Opposition leader after the election conceded that point.

While Ardern avoided answering the question directly, Davis stated his leader would be around for longer - for almost two decades, even: "we'll back her right through until 2035, when she's probably had enough of being prime minister".

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The wide-ranging interview saw Owen pushing the Labour leadership duo hard on questions from tax, railway to Auckland Airport, tikanga Maori prisons being back on the cards and whether Davis would step aside for another deputy prime minister if Labour formed a coalition to lead the country.

Ardern once again faced questions about how she became the Labour leader but reiterated she was genuine about previously having no plans to lead.

Owen pressed her about the fallout over Greens leader Metiria Turei's admission of once enrolling in a different electorate to the one she lived in and the impact it would have on Labour, but Ardern said it was a Greens issue and theirs to deal with.

When asked if Labour would honour Andrew Little's promise to not introduce any new taxes in the first term, Ardern said "this is a new leadership team, we'll bring a different stamp and there will be different ideas in there. But beyond that, people will have to wait and see".

Ardern pointed out the new leadership team had only been in place for 72 hours and needed some space to have a review about the party's direction.

However, while she did confirm the party had committed to remaining within fiscal parameters set in the Budget Responsibility Rules, she wouldn't confirm if Labour's infrastructure announcement to be made on Sunday in Auckland would be about rail to the city's airport.

"Oh, you can probably put a wager on that if you'd like, but you'll have to wait and see till tomorrow," Ardern said.

Davis told Owen a tikanga Maori prison was a possibility again but said getting rid of privately-run prisons would be a longer process, as the cost of breaking contracts would have to be weighed up.

When asked if he would step aside as deputy prime minister in a coalition for an MP from another party, Davis said he would "absolutely" take one for the team.

"I'm not going to get in the way of Jacinda being Prime Minister."

Davis also said Labour was preparing policy for Maori voters before the elections and that his electorate, Te Tai Tokerau, deserved quality over quantity.

On the issue of a referendum on Maori seats remaining - promised by NZ First leader Winston Peters, a potential coalition partner - Ardern said "Maori have not raised the need for those seats to go, so why would we ask the question?".

She was backed up by Davis, who said "Those seats were foisted upon Maori back in the 1860s just to really control our voting power, and we've become quite fond of them, to be honest, so we really don't want them to go".

Owen closed by asking about the percentage of the vote Labour needed to hit a mandate to form a coalition government.

Although she said voters had a right to know what to expect, Ardern said the figure was "totally unpredictable" and Labour would "focus on being in the strongest position possible".

 - Stuff