Campaigning for New Zealand’s September 20 election is set to begin in earnest following today’s formal dissolution of Parliament, with all indications pointing to a comfortable win for John Key’s conservative National Party government.

Key’s commanding position seems particularly impressive from an Australian perspective, as his defeat of Helen Clark’s Labour government in November 2008 came less than a year after Kevin Rudd took office. Whereas the ALP crashed in its first bid for re-election and burned in its second, Key looks to be on course for one of the most impressive victories in his country’s recent history.

The timing of the election neatly coincides with an economic upswing that has sent the country’s unemployment rate below Australia’s and slowed the flow of Kiwis to our own shores. The opposition leader, David Cunliffe, has struggled to make an impression since assuming the Labour leadership a year ago, trailing Key in preferred prime minister polling by a factor of four to one. Like its Australian counterpart, New Zealand’s Labour Party has suffered a long-term loss of support to the Green Party, on which it will certainly have to rely if it is to cobble together a parliamentary majority — presenting the National Party with a handy rhetorical weapon.

The election will be the seventh held since New Zealand replaced its British-style single-member first-past-the-post electoral system with a proportional representation model imported from Germany. Under the Mixed-Member Proportional (MMP) system, voters are given both a constituency and a party vote, with 71 local constituency members to be supplemented by around 50 top-up members from party lists, to achieve an overall result proportional to the national party vote. The uniquely New Zealand twist to the system is that seven of the constituency seats are reserved for Maori representation.

Whereas minority government seems to strike terror into the heart of Australia’s political culture, New Zealanders have grown comfortable with an electoral system, which in nearly two decades has delivered nothing else. However, the National Party goes into the election hopeful of breaking the drought, having just fallen short at the 2011 election with 59 seats out of 121.

While proportional representation theoretically requires a majority of votes to obtain a majority of seats, MMP does not in practice set the bar quite that high. This is due to the 5% threshold that must be cleared by parties that fail to win constituency seats in order to be eligible for party list seats. In 2011, only 3.4% of the vote went to parties that didn’t make the cut. However, that figure could be quite a bit higher if New Zealand First, currently the fourth-largest party in Parliament, falls below the threshold. This would lower the bar for a parliamentary majority perhaps as far as 46%, which on current polling looks more than achievable.

The chart below shows the polling trend of the six largest parties over the current parliamentary term, using bias-adjusted results from five pollsters (with due credit here to the Wikipedians who assembled the data in one place). The results are exactly as a government would want them to be, with a tolerable dose of mid-term blues having ended with a decisive surge during the election year. Based on the present position of the trend, the National Party is approaching double Labour’s vote, at 50.6% to 26.4%, with the Greens on 11.9% and New Zealand First not quite clearing the bar at 4.8%.

Should the government nonetheless fall short, there seem likely to be two or three right-of-centre crossbenchers whose support it can take for granted. Beyond that though, life will start to get complicated.

Since the last election the National Party has had the support of the three members of the Maori Party, which provides the government with two junior ministers. Perhaps for this reason, the party seems to have fallen on hard times. Its accommodation with the government has given rise to the rival Mana Party, which comfortably outpolled it at a recent byelection. Any seats the Maori Party loses to either Mana or Labour will harm the government’s cause, and the chances of this happening have been considerably boosted by the retirement of two of its sitting members.

Mana has entered a curious joint-ticket alliance with a well-funded entity called the Internet Party, whose founder Kim Dotcom (birth name Kim Schmitz) has won international renown as the founder of the barely legal file-sharing services Megaupload and Mega. The party’s philosophy is of a piece with the “pirate” parties that have established niches for themselves in various parts of Europe, and its only obvious point of unity with Mana is that neither is a natural ally of the National Party. Nonetheless, early indications for the alliance have been promising, with polling suggesting it stands to win around three seats, perhaps including one for Dotcom.

As has so often been the case during its two-decade history, the wild card is New Zealand First, the vehicle for mercurial parliamentary veteran Winston Peters. Polling has had the party tracking below the threshold for most of the present term, but it appears to be coming home with a wet sail. Despite the National Party’s apparent dominance, Key will still be having sleepless nights at the prospect of relying on the unpredictable Peters, who has backed both major parties at various times in the past, and invariably proved a troublesome ally.