Two current Labour list MPs will lose their seats in Parliament if the results of a Herald-compiled Poll of Polls are duplicated on election day in November.

The Herald's time-weighted rolling average of the results of New Zealand's major political polls shows Labour's support having dropped by more than three percentage points since the last such calculation in early July.

The fall in support now puts several Labour MPs who do not hold an electorate seat at risk of not making it back to Parliament.

Assuming Labour does not lose any electorates it currently holds, Stuart Nash and Steve Chadwick, who are ranked at No 27 and No 34 respectively on Labour's list, are the most vulnerable MPs.

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A further fall in Labour's support would thrust other MPs, such as Rick Barker, Carmel Sepuloni and Kelvin Davis, into the danger zone.

The Greens appear to be the main beneficiary of Labour's slide, having picked up nearly three percentage points since July.

National has gained just one percentage point over that period. That suggests it has hoovered about as many votes off Labour as it can hopefully expect to get.

However, National's rolling average of close to 54 per cent would enable the party to govern alone with a comfortable 11-seat majority.

The Herald Poll of Polls comprises results from the Herald-DigiPoll survey, the One News-Colmar Brunton poll, the 3News-Reid Research survey, the Roy Morgan Research poll and the Fairfax Media-Research International Poll.

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 have passed since the end of the survey period for a particular poll, then that poll is no longer included in calculations.

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.

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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.

Act would retain just two seats - enough to return party leader Don Brash and John Banks, assuming the latter won the Epsom seat. Act's deputy leader, John Boscawen, would miss out.

Such an outcome would see Act returned to Parliament - but with none of the six MPs who have represented the party in the current Parliament.