Green Party leader James Shaw says a new poll which saw the party plummet below the threshold needed to get into Parliament is disappointing and is appealing to the party's voters of past elections to get back behind it to ensure it returns to Parliament.

The Green Party plunged to 4.3 per cent in the 1 News Colmar Brunton poll, the first since former Green co-leader Metiria Turei stepped down during scrutiny of her admission to welfare fraud in the 1990s.

That is below the 5 per cent threshold needed to get into Parliament for parties which do not have an MP with an electorate seat.

In the same poll, Labour rocketed up from 24 to 37 per cent under new leader Jacinda Ardern. Ardern had rocketed up to 30 per cent as preferred PM, even with National leader Bill English.

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Green Party leader James Shaw is appealing to the party's voters of past elections to get back behind it to ensure it returns to Parliament. Photo / Mark Mitchell
Green Party leader James Shaw is appealing to the party's voters of past elections to get back behind it to ensure it returns to Parliament. Photo / Mark Mitchell

Labour is now seven points adrift of National, which was also feeling the strain of the tumult of past weeks, dropping from 47 to 44 per cent. Both parties would need NZ First to form a government but Labour would also need another support party - without the Green Party to turn to. Its votes would be wasted and would not count.

Shaw said it was clear Ardern had a "huge impact" on the Labour Party's fortunes and he congratulated her for that.

"I think what that means is a lot of soft voters who used to vote for Helen Clark and then John Key will now look at the Labour Party and start to peel away from National. At the same time, you'll see people saying 'well, Labour is now looking like it can form a government but they're going to need a partner. And that's the Green Party."

On the poll, NZ First was down from 11 to 10 per cent. The Maori Party had nudged up to 1.7 per cent and Gareth Morgan's Opportunities Party had also inched up to 2.1 per cent.

Act was on 0.4 per cent and United Future did not register.

The 1 News Colmar Brunton poll of about 1000 voters has a margin of error of +/- 3.1 per cent.

The result is devastating for the Greens which until the ructions of recent weeks had been polling around 10-11 per cent and has not been around the 5 per cent mark since the mid 2000s.

It is now fighting for its survival nearly five weeks before the election. Shaw, a first term MP, will have to fight his first election as leader without the experienced Turei on hand.

Shaw said there was a lot of work to do to rebuild trust and credibility with the Greens' support base.

"I'm really disappointed but we've still got a long way to go and I'm pretty confident we can rebuild from here.

"You would have seen how dramatic the swings have been in the last few weeks and I think we can recover in the next few weeks.

"I'm going to appeal primarily to those people who supported us in 2011 and 2014 and say 'we could do with your support again.'"

Asked how it felt to drop below the 5 per cent mark, he said "it doesn't feel great, obviously."

"I was expecting that we were going to take a big hit because obviously the last couple of weeks have been very messy and if there's one rule in New Zealand politics, it's that voters hate that kind of messiness when it comes to political parties.

"But I am hoping people will look at our track record over the last 17 years and see this as a bit of a blip."

The Green Party support had spiked to 15 per cent in the last Colmar Brunton poll at the end of July.

That was in the immediate aftermath of Turei's admission she defrauded the welfare system as a solo mum in the 1990s by not disclosing flatmates.

That sparked a series of events including the change over from Andrew Little to Ardern as Labour leader after Labour's polling dropped to the low 20s.

Turei stepped down as co-leader on August 9 and has opted not to return to Parliament after scrutiny of her admission and a further admission she had breached enrolment rules to vote for a friend took its toll.

She will stand in the Te Tai Tonga electorate to help the Greens get party votes.