Prime Minister Bill English is the politician who is most trusted to do what he says he will do, but new Labour leader Jacinda Ardern rates very closely behind, according to a new Herald-ZB-Kantar TNS poll.

Gareth Morgan, the leader of the Opportunities Party, came in a respectable fourth behind Winston Peters, ahead of many current politicians, and is poised to pick up some fractured support in the wake of the Green Party crisis.

The poll also shows that in the event of a Labour-New Zealand First coalition government after the September 23 election there is a strong preference for Ardern as Prime Minister over Peters, despite her inexperience.

The survey asked "which of these politicians do you trust most to do what they say they will do". English was trusted by 31 per cent and Ardern, after just a week as leader, by 26 per cent. New Zealand First leader Winston Peters polled 14 per cent followed by 
Gareth Morgan on 4 per cent.

Morgan was well ahead of ex-Green Party co-leader Metiria Turei, who registered only 2 per cent, United Future leader Peter Dunne on 2 per cent, Act leader David Seymour on 1 per cent and Maori Party co-leader Te Ururoa Flavell who failed to rate at all.

The poll began the day after Arden took over the leadership of the Labour Party and reflects the "Jacinda effect" which has seen her virtually match English in preferred Prime Minister polling and seen Labour rocket from the early 20s to the 30s in party vote support.

A gender differential in trust ratings is pronounced with Ardern being favoured by 30 per cent of women compared with 22 per cent of men, and English being favoured by 35 per cent of men compared with 27 per cent of women.

Peters is almost evenly trusted between men and women but Morgan is favoured by more men, 6 per cent, compared with only 2 per cent of women.

The poll was taken before Turei resigned as Green Party co-leader on Wednesday night following revelations of historic dishonesty over claiming a social welfare benefit and electoral registration.

While the Greens and Maori parties both had co-leaders during the polling period, respondents were offered only one leader, Turei and Flavell, the most senior of the co-leaders in terms of experience and party list ranking.

James Shaw is now the sole leader of the Greens.

The trust rating is not the same as Party Vote, however the relatively high rating for the Opportunities Party is also reflected in a reasonable showing for the party in two other polls this week.

The Opportunities Party polled 2 per cent in Newshub's Reid Research poll and 3 per cent in UMR's latest poll.

Under MPP, a party without any electorate seats, has to reach 5 five per cent before it can claim its Party Vote entitlement in Parliament.

Gareth Morgan was best known as an economist and author but his passion for conservation led him to call for cat controls.

Morgan may be hoping to get some momentum with his party launching its campaign today in Wellington.

The poll also establishes a firm preference for Ardern as Prime Minister in any coalition between Labour and New Zealand First, despite the gulf between her and Peters' relative experience in politics.

She has been leader for only two weeks and was first elected in 2008; he has led his party for 24 years, was first elected in 1979 and has been a Treasurer and Foreign Minister.

But only 13 per cent of respondents believed Peters should be Prime Minister in a Labour-New Zealand First coalition, 47 per cent thought Ardern should be, and 28 per cent said whichever party had the largest Party Vote.

Ardern has already ruled out any power-sharing deal with Peters.

• The online survey of 1000 respondents was conducted between August 2, the day after Ardern was elected Labour leader, and August 8. It has a margin of error of plus or minus 3.1 per cent.

• It is an online survey by ConsumerLink which runs on the Fly Buys panel of 120,000 active members, one of the largest in New Zealand.

• Sampling is nationally representative and is then post-weighted by age, gender and region to match the population but only those aged 18 and over are included.