The way Winston Peters has controlled the coalition talks and the refusal of National and Labour to collaborate has given his New Zealand First party maximum bargaining power.

The talks are set to step up a gear with discussions about ministerial posts - whether New Zealand First wants them at all and, if so, how many and whether they should be inside or outside of cabinet.

By leaving the issue of ministers until last, New Zealand First has maintained leverage throughout the process over policy.

With National and Labour kept guessing as to whether Peters wants a full coalition inside cabinet, a confidence and supply deal with ministers outside cabinet, or a more hand-off arrangement on the cross-benches, it has been impossible for the big parties to have trade-offs between ministerial posts and policy gains.

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That is different to 2005 when getting the plum role of Foreign Minister in a Labour-led Government before talks had concluded reduced the party's leverage over policy.

It is even more markedly different to 1996 when, from the outset, talks proceeded on the basis that New Zealand First would be part of a full coalition.

This time, Peters will have extracted and locked in policy concessions from both parties before turning to the type of arrangement and the type of jobs.

New Zealand First could opt for a different type of arrangement for National than for Labour.

For example it might see benefits in keeping greater distance from a tired fourth term National government than it would from possible coalition with a fresh first-term Labour Government.

There is one job Peters won't be asking for, despite suggestions by Act leader David Seymour, or getting and that is Prime Minister.

Denying Peters the top job is the one issue on which National and Labour have informally collaborated, almost like a mutual insurance policy.

As I detailed in the Weekend Herald in July, the issue of Peters as Prime Minister was canvassed in 1996 with National and Labour in quite different circumstances.

It was raised part way through the talks with National, on November 13 to be precise, during formal negotiations and after Peters and Jim Bolger had been asked to leave the room.

For Labour it was near the end of the process, and an informal approach was made to Helen Clark by Peters' youngest brother and negotiator, Wayne.

Peters having another tilt at the top job was a live scenario two months ago when Andrew Little was leading a much weaker Labour Party and heading south, and New Zealand First was on 13 per cent and it looked like it was heading north.

But Jacinda Ardern reversed those fortunes and Peters' party ended up with only 7.2 per cent. With that result, the prospect was dead on arrival.