OPINION: At every election night party at Chez Armstrong, an elderly gent from the Tory Ohariu contingent turns up. He plonks himself in the midst of all the Wellington Central Lefties and loudly declares that during the day he placed his hand over his nose and voted for Peter Dunne as his electorate MP.

Dunne's perceived crime is that over the years he has been part of both Labour and National governments, so is therefore a traitor. Knowing that the National candidate won't stand a chance against Dunne, my Tory friend very reluctantly votes for him simply to keep the Labour candidate out.

This year, as well as some Nats putting their hands over their noses as they vote for Dunne, I suspect there will also be quite a few Greens, who won't have an electorate candidate of their own, doing exactly the same thing as they vote for ex-police union boss Greg O'Connor.

DAVID WHITE/FAIRFAX NZ UnitedFuture leader Peter Dunne.

There has been a quaint tradition in Ohariu for a while now, not unlike the Epsom charade. National puts up a less-than-stellar candidate to shore up the party vote, which it has done most successfully, but at the same time the Nats give a nod and wink to Peter Dunne, who sees eye-to-eye with the Nats on most of their economic policies.

If Dunne came out as a Nat he would sit in the centre-left of that party. He's socially liberal, a fan of multiculturalism and opposes charter schools – though not stridently enough to embarrass the Government.

Yet despite Dunne being more centrist than many Nats, it's the Ohariu Labour candidate's job to make him out as more Right-wing than Genghis Khan. This is quite difficult if you sit on the right of the Labour Party, as Greg O'Connor seems to. As former head of the police union, PC O'Connor is not your usual PC Wellington Labour candidate.

As police union head, O'Connor has called for arming police and took a hard line on cannabis reform, as advocated by the Greens. With so many Ohariu voters forced to swallow dead rats this time around, is it time to rename the electorate Kioremate?

Yet recently, O'Connor, no doubt aware of the few thousand Green votes up for grabs, has softened his stance on arming the police – he was simply representing his members' views – and has gone from dubious to doobie-ist on the Greens' marijuana policy, saying that there are better ways to deal with cannabis than relying on the criminal justice system.

Both the recently engaged Green and Labour parties are aware of the strategic importance of Ohariu and realised it's not a good idea to stand against each other. Greens co-leader James Shaw has been careful to strongly nod in O'Connor's direction while telling Green voters it's up to them to decide. Shaw delivered exactly the same message to Ohariu Greens as John Key did to Epsom Nats, without a pesky teapot or cameraman getting in the way.

And it's difficult for National to criticise the Greens for not putting up a candidate when they refused to put up a candidate themselves in the Mt Albert by-election.

Ohariu promises to be a fascinating campaign, with Dunne having to ensure that he does not find himself to the left of O'Connor and O'Connor having to ensure that he does not find himself to the right of Dunne.

Labour is acutely aware how badly it has performed in heartland New Zealand. Last time, only blokey Stuart Nash in Napier and blokey Greg O'Connor's blokey cousin Damien in West Coast won electorate seats in the provinces.

But how 'provincial' and socially conservative is Ohariu? Though it's no Aro Valley, it has pockets of liberalism, which explains the Greens getting 11 per cent of the party vote last time.

If Peter Dunne can convince enough Nats that he stands to the right of O'Connor then the seat will be his. Meanwhile, if O'Connor can convince enough Greens that he stands to the left of Dunne then the seat will be his. Prepare the dead rats and let the contest begin.