National leader Simon Bridges has ruled out working with Winston Peters and NZ First after the 2020 general election.

National leader Simon Bridges has ruled out working with NZ First after this year's election, telling voters he can't trust the party.

Bridges' move, announced at a caucus retreat in Havelock North, sets the stage for a no-holds barred election campaign between the three parties that make up the Government and National.

It echoes a move made by then-oppositon leader John Key ahead of the 2008 election, when he too ruled out working with NZ First.

Bridges said Kiwi voters deserved to have a clear choice between National and the coalition - and that a vote for NZ First was a vote for Labour and the Greens.

"Our decisions will be about what's best for New Zealanders, not what's best for NZ First," Bridges said.

"I don't believe we can work with NZ First and have a constructive trusting relationship."

Bridges pointed to the decision of NZ First leader Winston Peters to sue several National Party ministers during coalition negotiations as a factor in the bad blood between the parties.

"I don't trust NZ First and I don't believe New Zealanders can either."

He said he was sick of the "charades" in the coalition - the various power plays and negotiations between the three governing parties.

PETERS: I COULD WORK WITH OTHER NATS

NZ First leader Winston Peters said he was "unfazed" by the decision and expected other National MPs in Bridges' caucus would want to work with him.

"The one thing New Zealand First is confident about is that if voters deliver that possibility [of a Government between NZ First and National], and if Mr Bridges doesn't pick up the phone, someone else within his caucus will do it for him," Peters said.

'Let me say this – he's got a lot to learn about politics. Narrowing your options can be the worst strategic move you will ever make."

"As Douglas McArthur said, there'll come a time soon when he'll when want to see me much more than I want to see him."

Bridges and Peters have shared a strained relationship since Bridges ascended to leader, with Peters repeatedly saying Bridges would be rolled by his caucus.

But Bridges said the matter "wasn't personal" and he wouldn't work with NZ First even if it was led by a different person.

He believed the election would be exceptionally closely-fought, but made clear that even if it was the difference between National governing and spending another term in opposition he would not be working with NZ First.

"MMP means every election is tight. And I think this will be the closest one ever," Bridges said.

BRIDGES SIGNALS EPSOM DEAL

Bridges said National would like to work with ACT in Government again, and would help the party get back into Parliament by asking National voters in Epsom to give their electorate vote to ACT leader David Seymour.

This allows ACT to enter Parliament despite the fact it is unlikely to gain more than five per cent of the party vote, the usual barrier.

"National's had a constructive working relationship with ACT while in Government. We developed the partnership schools model and worked together to reduce red tape. We would again be open to working with ACT and would encourage National supporters to give their electorate vote to David Seymour in Epsom and their party vote to National," Bridges said.

Seymour welcomed the news of "National's encouragement" but said he "always believed Epsom belongs to the voters."

"ACT and National worked together constructively in the last government and can do so again."

National also indicated a willingness to work with the Maori Party should it return to Parliament after the next election.

NZ First was spawned when Peters left the National Party in the early 1990s. It has worked with National once before in Government in the late 1990s but this ended in acrimony when Peters walked out Cabinet over the decision to privatise Wellington Airport.

In most polls since the election National would be unable to reach the 61-seat governing threshold without the potential support of NZ First.

But two recent 1 News/Colmar Brunton polls suggested National and ACT could govern alone, with NZ First out of Parliament.

Reproducing that poll result on election day will be the goal for Bridges - meaning NZ First wouldn't get a chance to govern with Labour or National.