POLL: A majority of New Zealanders do not fully believe what John Key says.

We may trust the prime minister, but we don't necessarily believe him.

A majority of New Zealanders do not fully believe what John Key says, despite rating him as a strong and effective leader whom they trust to run the country, the latest Fairfax Media-Ipsos poll testing voters' attitude to our political leaders shows.

Asked if they fully believed what Key said, 58.6 per cent said no and just 23.5 per cent yes.

KEVIN STENT/Fairfax NZ JOHN KEY: Asked if they fully believed what Key said, 58.6 per cent said no and just 23.5 per cent yes.

Ironically, in the poll taken before David Shearer stood down as Labour leader, the man who was widely criticised for his stumbles actually rated higher on that score than the PM - despite forgetting to declare a New York bank account containing more than $50,000.

About 33 per cent said they fully believed what Shearer said, although more - 43 per cent - said they did not.

Key's poor "believability" rating comes after a series of so-called "brain fades" over issues associated with Kim Dotcom and the Government Communications Security Bureau and the appointment of its head, Ian Fletcher, whom Key had known since childhood.

ROBERT CHARLES EX LEADER: While 33 per cent said they believed what former Labour leader David Shearer said, 43 per cent said they did not.

But it was the only category in which Shearer outshone the National leader, with the poll pointing to the reasons Labour MPs and the public lost faith in him.

Key's stand-out result came when people were asked if he was a strong and effective leader, with 59 per cent saying yes. Shearer rated just 22.8 per cent as someone who would make a strong and effective prime minister.

Just over half said they trusted Key to run the country against just over a third who saw Mr Shearer in the same light.

When respondents were probed for the reasons behind their views about Key some themes emerged, including that the pressure was getting to him, that he was coping - just - and that trust was slipping although he was doing well under pressure.

Typical negative comments included:

"I suspect the pressure he is under is making faults more obvious. I don't think there is a better opposition at this stage."

"Weak, always on the defence, and not very much on directions and purpose."

"The Tiwai smelter deal - John Key wants to keep that deal, which comes at a huge cost."

"Not as good as he has been, harder to trust him than it was. He doesn't appear as genuine as he once was."

On the positive side, respondents praised his reliability and solid performance, right up to those who could find no fault.

Comments included:

"I kind of think he's a smart guy. Looks like he's made it on his own and I definitely think that he's got the right attitude and he thinks big."

"I'm very happy to have someone with financial experience in charge, as the whole world is in economic recession."

"He's standing his ground. I like a politician that says one thing, ‘that's the guidelines they've been given', and they stand by that."

The telephone poll was of 1011 people with a margin of error of plus or minus 3.1 per cent.