Winston Peters says his party's own internal polling puts it higher than other polling results.

Winston Peters could be the key player in the next election.

Why so popular? The NZ First leader puts it down to his party's stance on the "elephant in the room": immigration.

Not that he takes any notice of recent Roy Morgan results, which has NZ First at 9.5 per cent for May. (National rose to three points to 45.5 per cent, ahead of a potential Labour-Greens alliance sitting at 41.5 per cent).

"We have our own polls that says that's nonsense," Peters said, implying the number was much higher.

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A recent Reid Research/ Newshub poll also showed an increase since November, with NZ First at 7.8 per cent.

"There's no doubt we're gonna corrode the National party base because people have got a guts-full," Peters said.

"We've spoken about things for a long time that have proven to be true, more and more New Zealanders are remembering who said that first."

New Zealand's levels of immigration were "disastrous economically and socially" - an issue NZ First had predicted years ago based on international research, he claims.

"When we were saying that, others were calling us xenophobic and racist. Look at the mess in Auckland now.

"Every infrastructural demand is at its very tipping point, whether it be roading, railways, hospitals, schools, it's all at a critical tipping point."

So it's no surprise the party's housing policy involves stopping speculation in land banking.

Peters is a fan of overseas speculators being hit with a "serious series of taxes", as well as a housing and land register to keep track of who owns what.

The party would also buy land and build state housing.

However, Peters points out that the Government has an obsession with Auckland housing. All they need to do, is "give it a chance to breathe" (that is, with an immigration policy).

ON THE BUDGET 2016: Peters wants a focus on exports.

"What we want to see in the Budget is the change in the economic approach, that demonstrates the understanding of how sound economies work. They work on wealth creation, on exports, on living within your means when it comes to imports.

"They would be policies to do with research and development and taxation. The word 'incentivisation' is deliberately used to rapidly grow our export capacity by making it worthwhile for people to take the risks to be exporters.

"Right now the support for our exporters is virtually zero and with an inflated dollar.

ON TAX CUTS: Not a fan.

"How can we afford tax cuts now?" Peters said. "This is a very shaky economy. One or two things go wrong and we're seriously going to be in a spin."

ON RAISING TAX BRACKETS: Even less of a fan.

"The country, with the level of debt we've got, cannot go borrowing to change tax rates."