Survey: Seven-seat margin on cards for Nats

National would be able to govern alone with a relatively comfortable seven-seat majority if the results of a Herald-compiled Poll of Polls are duplicated on election day in November.

As part of our election coverage, the Herald will be regularly publishing a Poll of Polls - a time-weighted rolling average of the results of New Zealand's major political polls.

Using a time-weighted rolling average allows greater weight to be given to more recent poll results while smoothing out short-term fluctuations and capturing the longer-term trends in party support.

The Poll of Polls comprises results from the Herald-DigiPoll, One News-Colmar Brunton, 3News-Reid Research and Roy Morgan Research surveys.

The rolling average is calculated from the results of polls conducted by those polling organisations during the past 50 days. If more than 50 days has passed since the end of the survey period for a particular poll, then that poll is no longer included in calculations.

Assuming the Maori Party retains four constituency seats and Act, United Future's Peter Dunne and the Mana Party each hold one such seat, the current rolling averages would produce a 123-seat Parliament.

With 65 seats, National would have an absolute majority of seven seats. National, however, might choose to continue including Act, United Future or the Maori Party or all three for longer-term strategic reasons.

Act would hold three seats - enough to return party leader Don Brash and deputy leader John Boscawen to Parliament assuming Epsom candidate John Banks wins that electorate seat.

Even with the backing of a re-elected Hone Harawira and the Maori Party's MPs, Labour and the Greens would fall well short of having the numbers to govern.