National's 50.4 per cent party vote in the latest Herald-DigiPoll survey is the sort of problem its Labour rivals would love to be wrestling with. But with National's overall majority still paper thin and its allies - Act, United Future, Maori and the Conservatives - all trapped within the dreaded margin of error, some pre-election gaming of the electoral system is inevitable.

In Epsom, National's candidate, Paul Goldsmith, has already assumed the prone position in favour of Act newbie David Seymour, continuing National and Act's decade-long rort of the MMP system in that seat. Doubtless there'll be a similar deal in Ohariu again to ensure the return of United Future's Peter Dunne.

But with the future of his Maori Party allies in doubt, John Key will still have to hold his nose and do a deal with oddball Conservative leader Colin Craig. On 1.5 per cent, the Conservatives are the highest-polling of National's bedfellows.

The dilemma facing Mr Key is that to do an Epsom in support of Mr Craig, he has to first find a "volunteer" among his North Shore MPs willing to take one for the team. Unfortunately, they all seem to be made of sterner stuff than Mr Goldsmith. North Shore is Mr Craig's home territory, but in quick succession, Mark Mitchell (Rodney), Maggie Barry (North Shore), Murray McCully (East Coast Bays) and Paula Bennett (Upper Harbour), have very publicly told the PM to look elsewhere.

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Former Labour Party president Mike Williams has come up with the obvious solution, mischievously proposing that Mr Key lead from the front and invite Mr Craig to stand in his own safe seat of Helensville.

As Mr Williams points out, Mr Key has no personal attachment to the seat and, as party leader, will automatically top the party list anyway.

MPs like the security of an electorate seat, especially when it's a safe one. It puts them at arm's length from party mandarins who, as keepers of the party list, hold the future of non-electorate MPs in their hands. For Mr Key, that is not a problem. He's clearly signalled that if he's not picked as captain, he's not playing any more.

This gaming of the system is not new. What is different this election is that instead of it being nudge-nudge, wink-wink, it's become formalised to the extent that Mr Key is promising to officially announce soon what rorts National intends to be involved in.

Like the internet-Mana Party stitch-up I criticised last week, in which millionaire non-citizen Kim Dotcom has paid $3 million into a joint campaign fund so his internet Party can coat-tail into Parliament on Mana leader Hone Harawira's electorate seat, these deals are throwing the sort of ordure at MMP that was associated with the unlamented first-past-the-post voting system.

Following last week's column, internet Mana started a campaign calling on Parliament to abolish the coat-tail rort it is using itself to get into in Parliament. It is also calling for an end to the threshold blocking parties with less than 5 per cent of the party vote from entering Parliament unless they win an electorate seat.

It does not specify what threshold, if any, it would put in its place, but quotes approvingly the 2 per cent barrier proposed by University of Michigan associate professor Rob Salmond in his submission to the Electoral Commission's 2012 MMP review.

In Mana's own submission, it proposed a threshold of "one seat (around 0.8 per cent party vote in the current Parliament)". This is the equivalent of about 18,000 voters.

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Mana said "any threshold, by definition, places barriers to new movements gaining access to parliamentary representation and protects incumbent parties".

But while Mana sees thresholds as a shortcoming in the system, the 1986 royal commission that proposed a 4 per cent threshold saw it as a necessary evil to ensuring effective and stable government.

The emergence of millionaires' vanity parties such as the Conservatives and the internet Party in recent times rather underlines the commissioners' fears.

In last year's Auckland mayoral elections, big-spending Mr Craig pulled in 42,598 votes from a voting pool a third the size of the parliamentary electorate. On Mana's 0.8 per cent threshold, that would have got his party two seats in Parliament, or more than six, if you scaled the votes up.

How many rich eccentrics, encouraged by the success of mining magnate Clive Palmer in gaining the balance of power in the proportionally-elected Australia Federal Senate, might leap out of the woodwork and seek to "buy" themselves a seat in the New Zealand Parliament if the threshold was 0.8 per cent?

The 2012 Electoral Commission Review cautiously proposed a 4 per cent bar, adding "it could arguably be lowered to 3 per cent on the basis of previous MMP results, without significant risk".

But it drew back, saying a 40 per cent reduction from the current threshold would be "a step too far". It suggested a further review, three elections on.

Instead, National decided to stick with the status quo and the rorts.