British elections are fascinating territory for psephologists. Analysing them is much more complicated than in Australia, for at least three reasons: there are far more seats; the first-past-the-post system produces more unpredictable swings because it encourages tactical voting; and the existence of three major parties makes it impossible to analyse results on a single dimension. So, for example, a swing from party A to party B can result in seats falling to party C, even if its vote hasn’t changed.

At the 2001 election, Labour with 40.7% of the vote won 413 seats, a majority of 167 over all other parties combined. A subsequent redistribution in Scotland abolished 13 seats, most of them Labour (since Labour held the vast majority of Scottish seats to start with), reducing that majority to a notional 160.

Of the 243 non-Labour seats, however, only about two-thirds are held by the Conservatives. They have 165, the Liberal Democrats 51, and a range of regional parties and independents the remaining 27 – 18 of them in Northern Ireland, which has a completely different party system to the rest of the UK. At this stage, expectations are that Labour’s majority will be substantially reduced, but not enough to threaten its hold on government. The polls have been showing Labour and the Conservatives very close (consolidated poll results are available here) but Labour should still win even if it falls slightly behind in the overall vote. That is because the voting system works to its advantage: the Liberals and the Conservatives, both being middle class parties, take votes from each other but (unlike in Australia) are unable to give them back as preferences.

For the enthusiasts, Martin Baxter’s site has a wealth of numbers, both predictions and historical data. Also useful is Adam Carr’s Psephos site, which applies an Australian perspective, at least to the extent of listing seats in order of swing required. His figures show the Tories needing a 6.2% swing to deprive Labour of its majority, and an 11.3% swing to win a majority in their own right. But with three parties and first-past-the-post voting, swing is a very tricky concept.