New Zealand prime minister John Key and his National Party are cruising towards an easy victory in tomorrow’s poll. Nonetheless, for those who are interested in the prospects for democracy in our part of the world it will still be a very important election.

Like other former British colonies, New Zealand inherited a system of single-member districts with first-past-the-post voting, which entrenched a two-party system. Combined with the lack of an upper house, it meant that governments wielded near-absolute power despite often having a minority of the vote.

By the 1990s, popular disaffection with this system reached such a level that, remarkably, it was able to effect reform even against the opposition of both major parties. A referendum in 1993 replaced first-past-the-post with the mixed-member proportional system (MMP) — basically the system used in Germany (with one notable difference that I’ll mention later) — to try to ensure that seats won would actually reflect votes cast.

Opponents of MMP predicted chaos and disaster if it was adopted, with the fragmentation of the party system and the end of stable government.

Not only has that failed to happen but New Zealanders have consolidated a party system that now looks very like ours, despite the different electoral system.

In 1993, in the last election before MMP, 30.2% of New Zealanders voted for minor parties. That rose to 38% in 1996 as people experimented with the new system, and as late as 2002 it was at a similar level, suggesting that a genuine multi-party system was in the making (see the official results here). But since then it has dropped right back — 19.8% in 2005, 21.1% in 2008, and going by the opinion polls maybe just over 20% tomorrow.

What’s more, the bulk of that minor party vote seems to be ending up with just one party, the Greens, who are expected to top 10%. One poll from Roy Morgan Research puts them as high as 14.5%.

The fact that MMP has led New Zealand not into the shoals of chronic instability but to much the same place as boring old unenlightened Australia is one reason voters are likely to vote against abolishing it — a referendum is being held together with tomorrow’s election. But the other reason is that MMP tomorrow looks like demonstrating that it can do what its opponents said it never would: give one party an absolute majority.

Opponents of greater democracy still have trouble understanding this point, but if voters fail to deliver one party a majority, you should be blaming them, not the system. The flip side of that is that if one party really does win a majority of the vote, a democratic system will follow suit and give it a majority of the seats.

That’s where John Key is heading tomorrow. The most recent polls (summarised by Antony Green) put National on between 49.5% and 50.9% of the vote, and if that holds up it will almost certainly deliver a majority.

It’s not quite as simple as that. A party with 50% should be well placed, since some parties will fall below the 5% threshold and their votes will be wasted (so 50% of the total vote might be 53% of the effective vote that determines representation). But some of the intricacies of MMP work the other way, and if you make a set of heroic assumptions — that several minor parties win their electorate seats, that the two Maori parties win most of the Maori seats (creating an “overhang”), and that mad Winston Peters gets his party back above 5% — then it’s possible that even a 50%+ vote for National would just fall short of a majority.

That’s what both Morgan and The New Zealand Herald are relying on in playing up the chance of another hung parliament. But it’s academic rather than real; it will only happen if ACT and United Future win their electorate seats, and they are both committed to supporting Key’s government in any case.

If tomorrow’s referendum votes to keep MMP, the government has promised a review of the system to tidy up some of its anomalies. That would be a good thing. An obvious matter for attention (although it seems unlikely to play a role this time) is the rule by which even one electorate seat qualifies a party for list seats, even if it’s well below the threshold — unlike the German model, where three electorate seats are required.

But despite such quirks, MMP has demonstrated that the system can be democratised without the sky falling in. Unfortunately there seems little chance that Australia will take the hint.