National's polling has barely flickered in the three weeks since the Dirty Politics book was launched and the party could still govern alone on 50.1 per cent in the latest Herald-DigiPoll survey.
Prime Minister John Key told the Herald the results reflected "a huge fatigue factor" with Dirty Politics.
Labour continues a slow decline, now at 23.8 per cent, and its support among males has fallen to 18.4 per cent.
New Zealand First continues a slow rise to 6 per cent, up 1 point, and would bring in seven MPs - one less than it has now. The Conservatives have risen by 0.5 to 3.8 per cent but unless they cross the 5 per cent threshold, or win a seat, they won't make it.
The Greens are unchanged on 11.4. Internet Mana is up fractionally and would still bring in four MPs if its leader, Hone Harawira keeps Te Tai Tokerau.
The Maori Party is down to 0.4, Act is on 0.4 as well, and United Future is on 0.3. The popularity of Mr Key has gone up a little in the past week.
David Cunliffe's ratings as preferred PM actually went up even more than Mr Key's, the likely result of greater exposure he is getting in the election campaign and a capable performance in the first televised leaders debate.
National would need 61 seats to govern and the poll result would deliver it 63. With current support partners Act, United Future and Maori Party it would have 66. Labour, the Greens, Internet Mana and New Zealand First would have 55.
The common wisdom is the party in government takes a hit in an election campaign as other parties get greater publicity. But other parties haven't got much exposure this campaign. It has only been in the past few days that the issues related to the book, based on emails of Whale Oil blogger Cameron Slater, have not dominated the political agenda.
The close association between former Justice Minister Judith Collins and Mr Slater was laid bare in the book. She resigned from Cabinet last week. In the Herald-DigiPoll survey that began the week Nicky Hager's book was published, National was on 50 per cent; the following week it was 50.7 per cent and this week it is on 50.1 per cent.
Mr Key said last night that "after four weeks of Dirty Politics, it is quite clear there is a huge fatigue factor and it is not a voter driver." He said he believed the capital gains tax was a "massive vote loser" for Labour because it was fraught with complexity and voters did not understand how it would work.
Joyce: Public interested in 'issues'
National Party MP and the party's campaign manager Stephen Joyce told Radio New Zealand the poll showed the public were more interested in the "real issues" of the economy and what that would bring to the country in terms of services.
He did not expect the party would be able to govern alone.
"Because under MMP you always need partners and I think we would fully expect not to be in a position to govern alone after September 20 and we will need partners and we will be looking to have partners.
"National would be happy to work with Act, United Future and the Maori Party, he said.
"The other two options for us, realistically, are the Conservatives and [New Zealand First]."Ideally there would be more than one option to make up a government, Mr Joyce said.
On the continuing fallout from Nicky Hager's Dirty Politics book, Mr Joyce said the public had processed the information quickly.
"They don't see it and won't see it as big an issue as other people did."
Labour's King: "Polls overstate National's figures"
Labour Party campaign spokeswoman Annette King told RNZ polls were "incredibly volatile".
"We're waiting for the poll of polls and that's election day."
Historically polls had overstated National Party's figures by about 6 per cent, she said.
"So the results you're seeing in these polls won't necessarily reflect the results on election day.
"Also historically in these polls Labour is understated."
The full party vote results
(compared with last week)
National 50.1 (down 0.6)
Labour 23.8 (down 0.3)
Greens 11.4 (no change)
NZ First 6 (up 1)
Maori Party 0.4 (down 0.6)
Internet Mana 3.5 (up 0.1)
Conservatives 3.8 up 0.5)
Act 0.4 (up 0.1)
United Future 0.3 (up 0.1)
PREFERRED PRIME MINISTER
(compared with last week)
John Key 68.9 (up 1.1)
David Cunliffe 14 (up 2.2)
Winston Peters 6.4 ( down 1.8)
The poll of 750 eligible voters was conducted between August 28 and September 3. The Party vote is of decided voters only and 7.4 per cent were undecided. The margin of error is plus or minus 3.6 per cent.
- Additional reporting Rebecca Quilliam