The Prime Minister has dismissed the effect of foreign buyers on New Zealand house prices.

"Frankly, it's a peripheral issue," said Bill English as he was closely questioned on the issue today by Tristram Clayton on NZ Herald Focus in the wake of the first televised leaders' pre-election debate last night.

English also suggested the Government needed to review the no-surprises rule, after he was asked how details of New Zealand First leader Winston Peters' superannuation were made public.

The Prime Minister deflected discussion of the 1 News-Colmar Brunton poll putting Jacinda Ardern and her Labour Party ahead of him and National.

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He said the voters would decide.

English and Clayton sparred on whether New Zealand was in a housing crisis, whether English regretted not attacking it soon enough, and what influences house prices.

Clayton said the register of foreign buyers recorded only those with New Zealand tax residency, and not those who bought through a New Zealand trust or business.

English said those registered comprised only 3 per cent of sales and had only a very small influence on prices.

"The prices are flat to falling. The thing now is how are we going to make sure the 200,000 houses that we need get built.

"And through our work with the councils, through or work with the construction sector that is now well underway, we funded the infrastructure here in Auckland, three hundred million [dollars], in Hamilton three or four hundred million. So that plan is now rolling out.

"I'm satisfied we did attack it early and hard. This is a big, hard problem. It's happened all around the world. We've had more success than most countries in cracking it and as we look out ahead we are going to see people, they are going to be able to envisage getting into the house that they want."

When asked about the release of Winston Peters' superannuation details, English ruled out the leak having come from his ministers or anyone connected with them.

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Clayton inferred that the leaker must therefore be a staff member of the Ministry of Social Development or the Inland Revenue Department.

"That's a matter for them," said English.

"Ministers handled it very professionally. They may have been better not to have been told about it ... we should look at those rules."

Political commentator Vernon Tava said English and Ardern were very evenly matched in last night's debate and he believes there was no clear winner.

Tava says traditionally it's the challengers who win the first debate and the next two head-to-head clashes could well be more important in the run-up to the election.

He says English would have been rocked by the poll result, which was announced just an hour before the debate started, but he held his own.

At the same time Ardern did well too, particularly with her references to "my generation".

Tava says the one certainty of this election campaign is volatility.