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Labour, in fact, has dropped a little - 1.3 points to 25.2 per cent - although leader David Cunliffe's popularity has risen.
The Greens have jumped 3.8 points to 13.7 per cent which would give them 18 MPs, boosting their numbers by four. National has fallen by 4.9 points to 50 per cent.
There has been a marked fall in the numbers who think the country is heading in the right direction, down from 57 to 51.1 per cent. National would still be able to govern alone based on this poll, whether or not its current support partners, the Maori Party, Act and United Future, were returned.
New Zealand First polls just under the 5 per cent threshold at 4.7 per cent and would not be returned to Parliament on this poll result, although several recent polls have the party just over it.
In a hypothetical scenario, if NZ First were to make the threshold by taking 0.7 support from the Conservatives, it would be a lot tighter, with National being able to govern with a majority of only one and requiring partners for any degree of comfort.
In this poll the Conservatives are up 1.4 points to 2.6, and not in Parliament without an electorate seat. At 2.1 per cent, Internet-Mana leader Hone Harawira would bring in two other MPs, Laila Harre and Annette Sykes, assuming he keeps his electorate seat.
Labour had a successful campaign launch in early August, promising free doctor visits to pensioners. But it appears not to have paid off in the poll with support among older voters declining.
The Greens launched their campaign with a $1 billion package to address child poverty, setting a new top tax rate of 40 per cent, and promising students free public transport in off-peak hours.
In the preferred prime minister stakes, John Key has fallen 8.5 points from the last poll to 64.8 per cent, back to where he was before his unusually high ratings in July following a particularly bad patch for Mr Cunliffe.
Mr Cunliffe has gone up 4.1 points to 14.6 points, a reflection possibly that he is getting a higher profile through his campaign, although the party isn't getting any pay-off.
Its messaging and everybody else's may be being drowned out by the volume of political fallout from the Hager book.
The book suggests a close association of National MPs and advisers with right-wing attack blogger Cameron Slater and has consumed most of the political oxygen in the past week. The book was released last Wednesday and DigiPoll began polling on Thursday.
Approval for Mr Key's performance as party leader is high with 59.6 per cent rating it as superb or satisfactory, 23 per cent average and only 16.6 per cent as poor or bad.
Mr Cunliffe's performance as party leader was rated as superb or satisfactory by 19.2 per cent, average by 43. 2 per cent and poor or bad by 31.9 per cent.
The poll of 750 respondents was taken between August 14 and 20. The party vote results are of decided voters only. Undecided voters were 12.5 per cent. The poll has a margin of error of plus or minus 3.6 per cent.
National 50 (down 4.9)
Labour 25.2 (down 1.3)
Greens 13.7 (up 3.8)
NZ First 4.3 (down 0.3)
Maori Party 0.7 (up 0.2)
Mana-Internet 2.1 (down 0.1)
Act 0.6 (up 0.6)
United Future 0.4 (up 0.4)
Conservatives 2.6 (up 1.4)
Aotearoa Legalise Cannabis (down 0.1)
Preferred Prime Minister
John Key Nation 64.8 (down 8.5)
David Cunliffe Labour 14.6 (up 4.1)
Winston Peters NZ First 5.1 (down 0.4)
Russel Norman 3.5 Greens (up 1.5)
David Shearer 1.5 Labour (down 0.7)
Helen Clark 1.4 former PM (up 0.9)
Seats in the house
NZ First 0
Internet Mana 3
Maori Party 1
United Future 1
- Based on the assumption that the Maori, Mana, United Future and Act parties keep one seat.
The poll of 750 respondents was conducted between August 14 and 20 and has a margin of error of plus or minus 3.6 per cent. On the party vote questions 12.5 per cent were undecided.