Labour and National are neck and neck as they head into the last week of the campaign, the latest Herald-DigiPoll survey shows.
But polling finished on Wednesday night, before National leader Don Brash plunged his campaign into crisis by admitting he knew that Exclusive Brethren were producing anti-Government and anti-Greens pamphlets, having earlier denied any such knowledge.
The poll would give Labour and National 50 seats apiece, unable to govern alone.
But the numbers delivered to New Zealand First and its new post-election position announced this week - favouring the party with the most votes - would give Labour the advantage and the ability to form a Government.
Labour is just fractionally ahead with the support of 40.6 per cent of voters (down 2.8 on last week's poll) and National with 40.1 per cent (up 1).
Labour - as the highest polling party - and the Progressives with 51 seats would be able to form a government with the support of New Zealand First's nine MPs.
Labour and the Progressives would have another option to form a Government. It could do so without New Zealand First's support, but it would require both the Greens and the Maori Party. This is the third successive week in the Herald-DigiPoll survey that the gap has narrowed between the two main parties. Two weeks ago, the gap was 9.3 points, last week it was 4.3 and now it is 0.5.
Sections of those polls showed considerable volatility, particularly with the National vote, but that is not evident this time.
The swings and the slides of the previous two polls had stopped, said DigiPoll director Gabriel Dekel.
The difference between the two parties in the first four days of polling were virtually the same as the overall poll.
New Zealand First is on 7.1 (up 0.5); Greens 5.6 (up 0.6); Maori Party 2.8 (up 1.6); Act 1.9 (up 0.2); United Future 0.7 (down 1); Progressives 0.4 (up 0.3); Destiny 0.3 (down 0.1); and Christian Heritage 0.1.
Under this poll, Act would disappear unless it won Epsom. And if it did win Epsom it would affect government formation.
The Labour-Progressive-New Zealand First scenario would be impossible.
Labour would not be able to form a government without the support of the Greens or the Maori Party.
For preferred Prime Minister, the poll shows: Helen Clark up 1.9 points to 54.7 per cent; Don Brash down 2.4 to 34.8. New Zealand First leader Winston Peters is up by 0.3 to 9.3.