New Zealand's free market economy is what is really at stake in the post-election negotiations to form the new Government.

The extent of NZ's openness to the world, immigration and trade have all been on the negotiating table in Wellington this week.

NZ First leader Winston Peters says he is intent on new policies that will result in the "economic and social progress of this country".

But Peters' authority to wrench substantial change in New Zealand is overstated.

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His own policy platform was rejected by nearly 93 per cent of New Zealanders.

That does not give NZ First - with just 7.2 per cent of the vote - the mandate to change the major policy settings that both National and Labour have had in common since 1984 (give or take some differences at the margins). NZ First's policies to limit foreign ownership and immigration, change monetary policy settings and the scope of NZ's free trade agreements are a major challenge to the status quo.

It is true that Peters has maximum leverage in these final days of the post-election negotiations.

In such circumstances, it would be tempting for the major political parties to simply cut a deal for power.

But it is important that National and Labour do not lose sight of the policy settings which have served successive New Zealand Governments both before and after the global financial crisis, and have underpinned offshore investor confidence in this country, its companies and institutions.

Anyone who travelled with Helen Clark or John Key to regional forums like Apec or the East Asia Summit will have heard each leader speak off a remarkably similar script.

Both leaders promoted regional integration, New Zealand's open labour market and willingness to secure free trade agreements, and also positioned New Zealand as a magnet for investment and immigration.

This matters, and it is not something that should be changed at will. Certainly not without substantial policy debate and agreement from the majority of New Zealanders.

Next week we will know how successful Peters has been in asserting NZ First's ambition for regime change in New Zealand.

The Peters prescription has been well-telegraphed this past week.

Bill English and Jacinda Ardern have been careful to maintain confidentiality as to the substance of their respective talks (no doubt out of fear of provoking the mercurial Peters to turn against them). Meanwhile, the NZ First leader has indicated that the level of foreign investment, monetary policy and housing affordability were among his party's key priorities.

There is obviously room to debate and modify policy in each of these areas.

But whichever of the pair emerges as Prime Minister next week, they would be doing New Zealand a disservice if they adopt NZ First's agenda. They have a responsibility to ensure their own party's policies are well to the fore and to ensure that confidence in New Zealand is maintained.

Yesterday, Peters told the Press Gallery that his negotiating team had worked overnight and early in the morning to get "as much completed in terms of summations both for the caucus' and the board's point of view.

"That includes doing the fiscals as far as we can go and making sure that we will have a very clear idea of what we need to inquire of the other parties to make sure there is no doubt as to the sum of our discussions."

It is important that NZ First - whose board will join Peters and his caucus on Monday to discuss the rival policy dossiers - does not rush to a conclusion.

National, Labour and the Greens should take a similar approach. Fiscal costings must be done and a coherent agenda forged.

When it comes to NZ First's choice as to which major party forms the next Government, Peters will be damned either way.

That's something he admitted at one of the many post-talks interviews with news media when he said his party was between the "devil and the deep blue sea".

To some extent, this is his own fault for setting negotiating deadlines that could not be met.

But it is also a recognition of the fact that 7.2 per cent of the vote does not give him a 100 per cent mandate.

In his bones Peters knows this.