The common assumption is that the first-past-the-post voting system will produce Commons majorities for a single party, and that coalitions are likely only under proportional systems, as in Germany, Ireland etc. That has been the usual result in Britain. But it is not automatic under first-past-the-post, as the last two Canadian elections show. No single party formed a majority in Ottawa after the 2004 contest, and, on Monday, although the Conservatives made big gains at the expense of the Liberals, they still fell 31 seats short of the 155 needed for a bare overall majority. The reason is that, instead of two dominant parties, Canada has four competing parties.

Britain now has at least a two-and-a-half-party system. The last election when Tories and Labour together won more than 80 per cent of the votes cast was in 1979; it was a mere 67.5 per cent last May. But the Lib Dems and others had 92 MPs last year, more than double the maximum from 1945 to 1997. This alone creates a formidable hurdle for the Tories to surmount in one go at the next general election, as they seek to go from 198 MPs up to 324 for a bare majority.

But Labour cannot count on the electoral system being as helpful as in the past. Boundary changes will cut its majority of 66 (ignoring the forthcoming Dunfermline & West Fife by-election) to 50 or less. And Labour holds a large number of seats with majorities of under one thousand. It would not require a big swing from Tories to Labour for there to be a hung Parliament.

That is why an outright majority for Labour or the Tories looks less likely than a hung Parliament. But that covers a wide range of outcomes, from Labour just falling short to the Tories being ahead. (According to the poll, a third expect Labour to be the largest single party in a hung Parliament, and a fifth the Tories. For more details, see www.populuslimited.com.) But would a hung Parliament be just an aberration, as in 1929 and 1974, before a return to single-party dominance? Peter Facey, of the New Politics Network think-tank, argued that the latest Canadian results suggest that: “With modern multiparty politics, the electoral system can no longer be relied upon to ensure a majority government.”

If hung parliaments were repeated, there would be strong pressure for PR but, in the short term, there would be the problem, as now in Canada, either of making a minority government work or of creating a coalition.

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