National Party supporters favour the Act Party most as a coalition partner, but not by much, according to the latest Herald DigiPoll survey.

The Greens are most favoured by all voters to be a partner of National in government with 38.9 per cent, compared with Act with 18.9 per cent, and the Maori Party on 17.8 per cent.

But among National supporters, Act is favoured more, with 30.7 per cent favouring it.

Prime Minister John Key is set to boost Act's chances of increasing its overall poll rating - 1.5 per cent in today's Herald DigiPoll survey - with a public meeting with Epsom candidate John Banks. A win by Mr Banks in Epsom is likely to boost party support in the wider country.

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Act is at present one of three support partners of the minority National Government, giving it five votes on confidence and supply along with the Maori Party and United Future.

Among National voters 27.7 per cent favour the Greens as the best coalition partner even though the Greens say it is "highly unlikely" they would give National their support on confidence and supply.

The Maori Party is most favoured by 21.1 per cent of National voters.

The question asked if National were to lead a Government with one other party, which would you prefer.

Other questions in today's poll also suggest that National and Labour voters are not toeing the party line on some issues, such as youth wages and work testing for solo mothers.

A majority of voters see youth wages more positively than negatively.

And National's hardline work-testing rules for women getting pregnant on the DPB also get voter approval. But they don't fall strictly down party lines.

Both policies have a significant amount of support from Labour voters, despite their being opposed by Labour.

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And a large number of National supporters believe the work-testing plan is too harsh.

Youth rates is one of the clear battle-ground policies this election with Labour and the Greens clearly opposing it and National and Act clearly supporting it.

National released policy last week that would extend youth wages for 16- and 17-year-olds to six months instead of three months.

It would also apply to 18- and 19-year-olds getting into work from a benefit and to 16- to 19-year-olds training in a recognised industry course. It is set at 80 per cent of the minimum wage.

Asked which was closest to their view, 54.7 per cent of respondents believed paying youth wages meant a young person was more likely to get a job; and 39 per cent believed that all workers doing the same job should be paid the same.

Among National supporters 68.3 per cent favoured youth wages with just 27.8 per cent believing equal pay was more important.

Among Labour supporters 49.8 per cent supported equal pay for youth while 44.8 per cent believed paying youth wages meant more jobs for young people.

One of National's most controversial policy releases this election has been its work-testing plans for women who get pregnant while on the DPB.

If her youngest other child is over 5, she will have to be available for work when the baby turns 1.

Of all those polled 52.9 per cent believed it was very good (14.2 per cent) or fair (38.7 per cent).

Among Labour supporters 37.1 believed it was very good (8.5 per cent) or fair (28.6 per cent).

But 29.6 per cent of National supporters believed it was too harsh, 20.1 per cent believed it was very good and 47.3 per cent thought it was fair.

National supporters do not ringingly endorse its policy to sell up to 49 per cent of five state-owned assets. While 80.6 per cent of National supporters back it, 18.3 per cent said they were less likely to vote for National because of it.