The Green Party co-leader says it is "highly unlikely" she will return to Parliament after the election.

OPINION: So the poll-quake has hit and it's a magnitude 9 on the political Richter scale.

And there is no doubt about the winner. Jacinda Ardern. She is barking at Bill English's heels as preferred prime minister – virtually neck and neck – and that is a massive sea change.

Green co-leader Metiria Turei is not blaming the poll for her shock decision to quit. Instead she pointed to the unacceptable pressure on her family since she admitted to lying as a student in the 1990s to get a higher benefit.

MONIQUE FORD/STUFF Jacinda Ardern has soared in the preferred prime minister stakes and is virtually neck and neck with Bill English.

She said the poll was not that bad . . . but surely it played a part in her shift from defiance on Tuesday to resignation on Wednesday.

READ MORE:

* Live: Metiria Turei resigns as co-leader of the Greens as party takes huge hit in polls

* Jacinda Ardern says she can handle it and her path to the top would suggest she's right

* The anatomy of a Labour leadership spill: Little exits stage Left pursued by the polls

* She has the x-factor - is that enough?

* Recap: Jacinda Ardern promises relentless positivity as Labour leader after Andrew Little quits

PHIL WALTER/GETTY IMAGES Jacinda Ardern has delivered Labour a real chance of victory.

No-one will say they are surprised by the seismic shift in Wednesday night's Newshub-Reid Research poll.

It was inconceivable that the positive headlines and the enthusiastic public reaction to Ardern would not have delivered a huge poll boost. Those with long memories can only compare her reception with the arrival of David Lange on the scene – only with an even bigger impact in her case.

In terms of a poll boost the only recent comparison is Don Brash's 2004 Orewa speech.

But there is a major difference.

Brash's speech had a negative as well as a positive aspect. As much as it rallied voters to National - and by far more than Ardern has achieved here – there was an equal and opposite kick-back from those who saw it as divisive and racist. And it left a bitter aftertaste.

Ardern's poll rise has been without any such controversy, based as it is on her personality and the sense that she has offered a solution to the incipient mood for "change".

Labour had detected the mood, and surveys had identified it too. But the Opposition could not capture it under Andrew Little or his three predecessors.

The only other question was where the votes would come from.

Would Labour simply peel back the 3-4 per cent it lost to the Greens when Metiria Turei dropped her "benefit bomb"? Or had there been a bigger landslide of votes away from the Greens as the crisis around Turei deepened, topped off by David Clendon and Kennedy Graham quitting. And would Ardern simply restore Labour's fortune to the 28-30 per cent level it had bobbed around at before the sudden slide over the past month or so?

The answer is fairly clear. The Greens have shed a huge amount – 4.8 per cent – and Winston Peters has shed 3.8 per cent some support too, albeit he is now the third party.

So far the damage to National has been limited.

But strategists in Labour argue that in such cases the first round effect is always to harvest votes from the minor parties. The second round effect – as it was with the Brash-Orewa phenomenon – is where votes switch between the two big parties.

Part of that will be the new found "stability" Labour is keen to talk up.

It's a theme National has immediately targeted with its talk of a "circus" on the Left and Labour being "joined at the hip" to the beleaguered Greens.

But in politics the trend is your friend, and Ardern and her deputy Kelvin Davis are riding high on the bandwagon at the moment.

Part of that is the "sexy party" that an election campaign often installs; the party that is trendy and fashionable that everyone is talking about.

At various elections the title has gone to the Greens, NZ First, the New Zealand Party, and even United Future or (very briefly) the Internet Party. Gareth Morgan and his Opportunity Party may have been hoping to get the "cool" tag this time around, but Ardern has claimed it unequivocally for Labour.

It has to be said though, that despite the sea change in Labour's fortunes the big political picture has not changed when it comes to the pivotal role of Winston Peters.

He is still sitting pretty to determine who will be king or queen after the election.

But even here things have changed in the last two turbulent weeks.

Now Peters and his party are third and have overtaken the Greens, though only just. That makes it so much easier for him to command second fiddle in a Labour-led Government and squeeze the Greens out of ministerial jobs.

But it also improves his negotiating hand with National and Labour.

A weak Labour on 24 per cent and National above 40 per cent it would have been a big ask for Peters to install.

But now he will be able to argue much more credibly that Ardern is an option - and that will put National on the back foot in coalition talks with him.

And remember perhaps the most significant shift in this poll and the public mood.

When it comes to the people's choice of preferred prime minister it is now a 50/50 call between Ardern and English.

- Audio courtesy of RNZ