Poll of polls: Smaller parties staring at the brink

It's white-knuckle time for the small parties, especially the Greens, whose poll-of-polls average last weekend fell below 5 per cent.

If the Greens don't get 5 per cent in the election that will be bad news for Labour.

Prime Minister Helen Clark on Monday downplayed that possibility: small parties gain when the spotlight goes on them in the election campaign, she said.

So goes the received wisdom: the combined vote for the two big parties goes down during the campaign, making more space for the minors.

In 1996, Act leaped the 5 per cent hurdle. In 2002, United Future's eruption stunned pundits and New Zealand First came back from near-death - both in large part due to National's collapse.

But actually parties go every which way, as the table shows.

The Maori Party is at 2.1 per cent but the main interest is in its performance in the electorate seats, not the party vote.

Focus on the combined Labour-National support over the coming weeks. If that holds up, small parties will struggle to build support.

The poll-of-polls chart is a bad omen for them. New Zealand First and the Greens fell in July as Labour and National at last came fully to grips with each other. If that contest remains hot, as is likely, voters' attention will be less likely to wander to the smaller parties.

One saver will be if big-party voters see a need to get a support party over 5 per cent.

Most likely example: Labour-leaners helping Greens.

* Each week the Herald examines an aspect of the poll-of-polls. The average at any point on the chart is of the four most recently published of the Herald DigiPoll, Colmar Brunton (TVOne), UMR (NBR), TNS (TV3) and BRC (Sunday Star-Times).

All five are in the mix at all times but each point on the chart represents a different combination of four of the five polls.