Election 2017: Labour leader Jacinda Ardern on campaign trail

Labour leader Jacinda Ardern and deputy leader Kelvin Davis after their caucus at Parliament Wellington. Photo / Mark Mitchell

Labour leader Jacinda Ardern talks to Newstalk ZB's Kerre McIvor

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Earlier today, Jacinda Ardern has put her deputy leader straight after he wrongly suggested Labour wouldn't introduce a capital gains tax until after the 2020 election.

Whether a capital gains tax will be introduced has been a key attack line from National and Labour's deputy leader Kelvin Davis has provided more ammunition after appearing on the AM Show this morning.

Labour's policy is to establish a tax working group to look at options, including a capital gains tax.

Previous leader Andrew Little said if a capital gains tax was recommended by the group, he would implement one only after taking that to the electorate at the next election.

Since taking over as leader Ardern has changed that position - saying she will act on recommendations before the next election in order to address the housing crisis. She has made clear a capital gains tax would not be applied to the family home.

However, this morning Davis said he "didn't know" if a capital gains tax could be introduced before the next election.

"We've got to have the tax working group make their decisions, and we'll come to the country with whatever they produce."

After visiting students at Mt Albert Grammar School in Auckland, Ardern told media she had spoken to Davis.

"He is certainly now very clear on our position. I have been really clear with Kelvin. He absolutely understands where we are at on that."

Ardern said she had been "absolutely clear" on her position.

"I have absolutely maintained our right and my right as leader to make sure that when that tax working group reports back, that I am able to act in government in the best interests of New Zealand to try and address the housing crisis.

"It is a different position to what the last Labour leader had. But it is something that feels very important to me - very important to the next generation trying to get into the housing market."

Ardern said she felt sitting on the recommendations of the tax working group until 2020 would be too long to wait, but voters would no doubt deliver a message on any changes at that election.

Asked if the capital gains tax could apply to businesses, Ardern said she didn't want to predetermine any recommendations from the working group.

"It is obvious to anyone that is listening to me that my focus is on the housing market."

Last month Davis showed a willingness to be his party's attack dog - calling Health Minister Jonathan Coleman the "doctor of death" and comparing Bill English's personality to that of a rock.