Winston Peters' talk of sitting on Parliament's cross benches after the election - rather than entering a coalition or propping up a minority government - has never sounded totally convincing.

It has been assumed that should New Zealand First end up holding the balance of power after September 20 that Peters would want to be a senior minister - as has been the case twice previously.

His desire for a top job may be further fuelled by the possibility the next parliamentary term might be his last before political retirement.

Peters, however, has led the Opposition charge on the "dirty tricks" allegations being levelled at John Key and Judith Collins following the publication of Nicky Hager's Dirty Politics.

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While this may help Peters to get his party above the 5 per cent threshold on election night, the more pleasure he takes in twisting the knife in the Prime Minister's back, the more difficult it will be to rationalise going into government with Key.

Given he has shown no great enthusiasm for propping up a Labour-Greens Government, Peters may not be kidding with his increasing talk of opting for the neutrality of the cross benches, thereby - as he says - foregoing political office and power, but "keeping the system honest".

But what does sitting on the cross benches actually mean? And is it possible for a political party to be entirely neutral as any decision not to back either National or Labour inevitably helps one or other of the major parties unless both have the same number of seats in Parliament.

Does it mean abstaining on confidence and supply measures and voting on an issue-by-issue basis when it comes to determining whether Government legislation will be passed by Parliament or not? Or does it mean voting confidence and supply, but staying outside a governing arrangement?

In part, it will hinge on the numbers. For example, if the centre-left bloc won 58 seats, the centre-right bloc took 56 and New Zealand First the remaining six, Peters could not abstain if - as kingmaker - he wanted a minority National Government to continue in power.

When asked last night what "sitting on the cross benches" entailed, he said everyone knew and he had never fielded a question on the subject from the audiences at his many public meetings.

He did confirm it does not mean voting confidence and supply and holding ministerial portfolios in a governing arrangement - the stance Peters took in 2005. But it would be useful for everyone to know a little bit more than that.