Preoccupied with the fate of government in Canberra, no one on the mainland paid much attention when, the week before last, Tasmania’s three party leaders reached agreement to increase the size of the state’s House of Assembly from 25 to 35. But with hung parliaments very much the topic of the day, Tasmania’s situation has some wider lessons.

On one level, providing for more Tasmanian MPs is an obvious move. Trying to staff two front benches from just 25 people is a hard task — the upper house is mostly full of independents, so it doesn’t help much. Liberals and Greens went to the last election supporting a return to a house of 35, and since they won a clear majority between them it was always likely to happen.

But this is politics, so consideration of political advantage is never far away. The size of the lower house was reduced in 1998 in a deal by Labor and the Liberals to try to shaft the Greens. It worked in the short term, but didn’t prevent the Greens ultimately returning to five seats and more power than ever.

If this year’s election had been held with seven members instead of five from each of the five electorates, it probably wouldn’t have changed the relative strength of the parties at all. According to Peter Tucker’s calculation, they would have finished at 14-14-7, up from 10-10-5, although a strong preference flow from the Liberals could possibly have given the Greens an extra seat in Bass at the expense of the ALP.

But a larger house offers more potential benefits for the Greens. It gives them more downside protection, since reducing them back to one or two seats becomes an almost impossible task, and it makes them overwhelmingly likely to win two or more seats in at least one electorate, an essential step to credibility as a major party.

More members per electorate will mean a more proportional result, making single-party government more difficult. Unless something changes radically in Tasmanian politics, it seems that a 35-seat house will give the Greens the balance of power on a more or less permanent basis for the foreseeable future.

How does this compare with the position in Canberra? Obviously, the Greens are much stronger in Tasmania than nationally; even with their strong result last month, their national vote is only a little over half what it is in Tasmania.

Interestingly, however, that’s because the Tasmanian Greens have mostly soaked up the votes of minor parties and independents. The two major parties don’t do a whole lot better nationally than they do in Tasmania: 75.9% between them in Tasmania; on the latest figures 81.6% federally (even counting the various components of the Coalition together).

So what makes majority government the norm in Canberra but now the exception in Tasmania is basically the difference in voting system. No party (or coalition) has won a majority of the primary vote in a federal election since 1975; no party has even got close since Labor won 49.5% in 1983. If seats won reflected votes cast, the current minority government would not be such a novelty; the major parties would have to adjust to rarely having the numbers in their own right.

During this year’s Tasmanian election, which delivered the Greens the balance of power and ultimately two seats in cabinet, Greens leader Nick McKim eschewed the term “hung parliament”, preferring to talk about a “power-sharing parliament”. Now that power sharing has come to Canberra as well, we need more of a debate about whether our electoral system really reflects what voters want, or whether artificially constructed majorities might do more harm than good.