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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.