National has opened up a big lead in the latest Herald DigiPoll survey as Labour feels the fallout from a tumultuous month.
It has 46.4 per cent support - a 7.7 point lead over Labour.
Labour's support, hit by allegations against Taito Phillip Field and calls for the party to repay taxpayers' money spent on its pledge card, slipped to 38.7 per cent.
The last time National held such a commanding lead was in early 2004 after leader Don Brash's Orewa speech attacking race-based policies.
The result from a poll of 751 people is a big change from recent surveys which have shown National and Labour neck and neck or National edging just ahead.
Until now Labour has appeared to be virtually unaffected by the prolonged Field affair and election spending row.
Two weeks ago, Prime Minister Helen Clark said she doubted the issues were having any effect outside the Wellington political "beltway".
Last night, a spokesman for the Prime Minister described the poll result as "not surprising given what we have been putting up with over the last month".
But he said Labour won the 1999 election with identical party vote support, "and it's two years until the next election".
National declined to comment, and a spokesman said the party didn't want to get into the habit of commenting on polls.
The poll was conducted as new allegations were being made against Mr Field, who yesterday broke his public silence to say he intended to stay on as Labour MP for Mangere.
Mr Field's decision to fight the allegations against him and battle for his position means National will be able to continue its attacks on Labour about him.
The other issue on which Labour has been feeling the heat - the Auditor-General's draft view that much taxpayer-financed party advertising for last year's election was unlawful - is also yet to be resolved.
National has tried to seize the moral high ground in the issue by paying back the $10,000 of its spending that was identified by the Auditor-General as unlawful.
Labour, like several other parties, has instead been arguing that the rules have been changed after the event.
And it has hinted that it might pass a law to validate the spending.
Other issues prominent since the previous Herald-DigiPoll survey in April include power blackouts in Auckland and other areas, an intense focus on child abuse after the deaths of infant twins Chris and Cru Kahui, and big increases in the price of petrol.
Of the minor parties, the Greens are the only ones in the new poll to top 5 per cent support - the figure which parties without electorate seats must achieve in an election to gain a place in Parliament.
They have 5.8 per cent, slightly up from their 5.2 per cent in the April poll.
New Zealand First has slipped from 3.9 per cent to 2.8 per cent, and relinquishes fourth place in the party standings to the Maori Party, which has risen to 3.4 per cent support from 2.1 per cent in April.
NZ First leader Winston Peters' personal support is also down - he now has 5 per cent support in the "preferred prime minister" poll, one point behind one of National's leadership contenders, John Key, who is in third position.
Helen Clark remains her party's strength with 52.4 per cent support as preferred prime minister, although that is lower than the 57 per cent support she had in April.
Dr Brash's support was unchanged at 22.4 per cent.