Key Points:

The political divisions and allegiances triggered by the furore over secret donations to New Zealand First and leader Winston Peters have had little effect on party standings in the latest Herald-DigiPoll survey.

Support for National, which has said it would not work with New Zealand First after the election, has risen slightly, by 1.4 percentage points, to 51.4 per cent of decided voters.

This would give it 68 seats in Parliament - enough for it to govern without a coalition partner.

Labour, which aligned itself with Mr Peters, is down 0.6 points to 35.7 per cent.

New Zealand First is up by 0.7 but to only 2.8 per cent - not enough for it to stay in Parliament after the November 8 election without winning an electorate seat.

The Green Party has slipped under the 5 per cent threshold, and at 4.9 per cent would also be a casualty without an electorate.

Mr Peters' standing in the preferred Prime Minister poll has fallen, by 1.6 points.

But Prime Minister Helen Clark and National leader John Key have also slipped.

The two main-party leaders are close as preferred PM, however, with Helen Clark down 1.9 points to 43.1 per cent and Mr Key down 1.1 to 45.5 per cent.

Their ratings have varied little since May.

Polling for the survey began in the week after the announcement of the election, when Helen Clark said it would be about trust, and finished on Wednesday, two days after Mr Key was found to have been not entirely truthful about the number of Tranz Rail shares he once owned.

During the past month, the privileges committee continued its inquiry into whether Mr Peters should have declared the $100,000 donation from billionaire Owen Glenn and by a majority ruled that he should have.

Parliament censured Mr Peters for knowing about the grant from the Monaco-based expatriate and not declaring it.

The issue most likely to influence voters this election is still the economy, cited by 28 per cent of those polled.

Law and order was again second (17.8 per cent), followed by tax cuts (16.5), leadership (12.3), hospital waiting lists (10.3) and global warming (6).

National's support is strongest in Auckland, where 55 per cent of those polled supported the party, compared with 51.4 per cent nationally.

Support levels for preferred Prime Minister differed between men and women - Helen Clark had slightly more support from women than from men, and John Key had a greater proportion of male support.

National's gender bias is reduced in this poll, and it has similar levels of support from men and women.

* The poll of 700 respondents was taken between September 15 and 24 and has a margin of error of 3.7 per cent. Undecideds totalled 11.1 per cent.