It’s tough being a third party in Britain

The British media are buzzing with excitement today after a spate of polls showing a surge in support for the Liberal Democrats.

Apparently boosted by the strong performance of their leader, Nick Clegg, in last week’s televised debates, the Lib Dems are registering support of around 29%, close to or possibly ahead of Labour and only a few points behind the Conservatives.

I’m skeptical of these numbers, as one should be of any sudden movement in the polls — especially for smaller parties. Similarly, opinion polls prior to the Tasmanian election showed the Greens with support in the high 20s. It turned out the swing to the Greens was real and significant, but the polls were greatly overstating it.

The comparison between Greens and Lib Dems is an interesting one. The Lib Dems start with two big advantages in their attempt to win a place at the table. Firstly, they’re coming off a higher base: at the last UK election, they were only 10.4% behind the Conservatives, whereas the Greens in Tasmania finished 15.3% behind the second placegetter, the ALP.

Factoring out the minor parties, the three-party votes looked like this (different sources all give slightly different numbers for the UK — I’m using Adam Carr’s figures):

The second advantage is that the Lib Dems are centrist in a way that the Greens are not, giving them much more freedom of manoeuvre. Whereas it was always going to be a stretch for the Liberals and Greens to talk to each other, neither side in Britain will refuse to talk to the Lib Dems, and the signs are they will happily deal with whoever makes a better offer.

But set against those two things, the Lib Dems have one big disadvantage: the electoral system is stacked heavily against them. The Tasmanian Greens got 20% of the seats with their 21.6% of the vote, but the Lib Dems’ 22% won them only a miserly 62 seats, or 9.6% of the total.

Even if the Lib Dems could knock one of the other parties into third place by votes, it’s almost impossible for them to overtake them in seats. It’s instructive to play with the BBC’s seat calculator to see just how big the handicap is. While Labour won a clear majority five years ago with just 35.2% of the vote, a Lib Dem vote of that magnitude could still leave them as the smallest party.

The problem is not just that the system of single-member constituencies discriminates against smaller parties; it also disadvantages parties, like the Lib Dems, whose support is relatively evenly spread. And because of first-past-the-post voting, it does so capriciously: people vote tactically, in ways no model can really predict.

It was suggested in Tasmania (on fairly thin evidence) that many voters just wanted a majority government regardless of party, but had no way of getting it because the major parties were so evenly balanced. In Britain, the contrary suggestion has been made that voters are so fed up with the established politicians that they are consciously setting out to return a hung parliament.

Whether they’re doing it deliberately or not, the odds are shortening that a hung parliament is just what they’ll get.