Bill English and Jacinda Ardern square off in their first leaders' debate on Thursday night.

OPINION: The earthquakes just keep coming. The latest 1 News Colmar Brunton poll is a massive jolt to the political scene and for the first time makes it a reality that there could be a change of Government in just three weeks time.

Labour is ahead of National – only by two points, but for shock value it may as well be 20, as stunning and as unlikely it would have seemed even just a few weeks ago.

The only difference is Jacinda Ardern. She has given voters a clear choice after years of Labour muddling through with leaders who never mastered that precious quality called cut through.

WARWICK SMITH/STUFF Next prime minister? Jacinda Ardern has given Labour a dramatic boost.

Even under all the scenarios where the pundits thought Labour might be in a position to put together a government after September 23, few added in the likelihood of Labour passing National in the polls. National's dominance for the last decade has been that complete.

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* Debate: How Bill English and Jacinda Ardern are preparing

* Mike Hosking, dressed in black T-shirt, asks Jacinda Ardern what she'll be wearing during leader's debate

Yet it reflects how things feel on the ground. Out on the street voters seem equally torn, the two camps dividing down two simple themes: either they think it's time for a change, or they buy into the view that change is risk.

BRADEN FASTIER/STUFF National leader Bill English, whose campaign has looked increasingly desperate.

And National's campaign has had the look and feel of the Clark government in its final term.

Ideology is out the window as the announcements come thick and fast: an extension to paid parental leave, $80 million on social housing, billions of dollars on new roads. It's felt like punch and counterpunch of promises from Labour and National.

It's not all over yet for National, of course – not by a long shot.

But the poll result couldn't have come at a worse time for English; on the eve of a crucial leader's debate, his first head-to-head with Jacinda Ardern.

He will be shattered by the result and the pressure of everything resting on his shoulders will be immense.

But English at least has one advantage he previously lacked – he now goes into the debate the underdog.