Labour is winning the battle of the big parties, but between them National and Labour look like destroying the Greens and NZ First in tomorrow's election, the latest Herald-DigiPoll survey indicates.
Labour is so far ahead it could run a majority Government on its own, if today's poll translates to votes.
Because of the poor showing by the minor parties, Labour, despite getting just 44.6 per cent support in this poll, could take more than half of the seats, assuming the poll is reflected on election day.
This would come about because minor parties that fail to reach the 5 per cent threshold needed to be allocated seats - including NZ First and the Greens - would command a joint 12 per cent.
Those votes would not count, so the proportion of seats would be decided on 88 per cent of the total cast, giving Labour 61 seats out of 120, well ahead of National, whose 37.4 per cent would deliver 51.
However, DigiPoll director Gabriel Dekel said the poll came with a caution that it could not be seen as a predicted result because of the extreme volatility shown in polling throughout the campaign.
Last week, the Herald-DigiPoll survey had Labour and National virtually neck and neck. Last night, a 3News-TNS poll showed Labour ahead of National by 1.8 points and a One News-Colmar Brunton poll put National ahead by 6 points.
"To get a correct picture when people are shifting their views so quickly, you need a high-speed camera," said Dr Dekel.
Quality control checks, in which respondents to this week's poll were contacted again after three days, showed that 20 per cent had changed their minds.
Dr Dekel noted that there was much higher participation of Maori voters in this survey. Especially big shifts were recorded among Aucklanders, women and the aged.
Labour appears to have made huge gains among women, from 45.4 per cent of them in the last poll to 50.8 per cent this week. Conversely, National's support among women has fallen, from 39.3 per cent last week to just 32 per cent this week.
National support in Auckland has dropped from 44 per cent last week to 39.5 this week.
And the proportion of support from the over-65s has virtually reversed: among that group last week 32 per cent supported Labour and 43.5 per cent National; this week Labour's support is up to 46.2 per cent and National's has dropped to 35.3.
A single-party majority rule scenario has been considered virtually unachievable under MMP, but unlike previous elections, in which exposure of smaller parties has lifted their support, this campaign has focused heavily on the tax-relief promises of the two juggernauts.
Tax is still rated as the single most important issue among voters, followed closely by health.
Today's poll reinforces the likelihood that small movements in small-party support could have a significant impact on the outcome of the election.
It records a decline in support for NZ First, down 2.6 points, and leader Winston Peters as preferred Prime Minister, down by 3.9 points.
The polling period directly followed NZ First's decision to talk to the party with the highest votes, and includes Mr Peters raising historical allegations against Tauranga rival Bob Clarkson.
The party vote results: Labour 44.6 (up 4); National 37.4 (down 2.7); Greens 4.6 (down 1); NZ First 4.5 (down 2.6); United Future 2.6 (up 1.9); Maori Party 2.3 (down 0.5); Act 1.3 (down 0.6); Progressives 1.1 (up 0.7); Destiny 0.9 (up 0.6); Christian Heritage 0.2 (up 0.1); Alliance 0.1; Legalise Cannabis 0.1.
In the preferred Prime Minister stakes, Helen Clark is on 55.1 (up 0.4); National leader Don Brash on 33.9 (up 1.5); and Mr Peters on 5.4 (down 3.9).
Of those polled, 52.6 per cent believed the Government was heading in the right direction compared with 41.3 who did not.
The poll was conducted between last Friday and Wednesday this week.
It did not capture potential damage from the Ombudsman's ordering the Government to release Treasury figures on Labour's student loan policy, nor response to last night's final leaders debate on TV3.
But it was conducted in the aftermath of Dr Brash's admission that he was given advance notice of the Exclusive Brethren's anti-Government campaign.
Volatility of the polls has been a feature of this election, particularly of National's support.
That was reflected within portions of the weekly polls the Herald has run during the campaign.
But since July, Labour has been ahead in all complete DigiPoll surveys and has not dipped below 40 per cent (it polled 41.26 last election) and National has rarely climbed above it.
In the past three elections, DigiPoll's final survey has been remarkably close to the election-day result.
* The poll of 1000 respondents has a margin of error of 3.1 per cent. The party vote preferences and preferred Prime Minister were for decided voters only.