London by-elections: what does 2008 tell us so far?

As with opinion polls, you can often tell more from council by-elections by looking at the pattern over several. There have now been four by-elections in London in 2008, so what is the picture so far?

There have been two Liberal Democrat holds with increased majorities (Fortune Green in Camden and Highgate in Haringey), one Liberal Democrat gain from Labour (Leyton in Waltham Forest) and one Conservative hold with a hugely cut majority over the Liberal Democrats (Cheam in Sutton).

All in all, a good picture for the Liberal Democrats with a net gain of one seat and vote increases in each contest: +13% in Leyton, +4% in Fortune Green, +4% in Cheam and +13% in Highgate.

The picture for the Conservatives is rather weak, with vote drops in three out of the four and certainly no sign of grassroots momentum building up ahead of May: -2% in Leyton, +2% in Fortune Green,  -12% in Cheam and -2% in Highgate.

Labour too have seen their vote drop in three of the four contests: -14% in Leyton, -2% in Fortune Green, +1% in Cheam and -1% in Highgate.

The Greens have stood in three of the four, with their vote falling in all of them: -4% in Leyton, -4% in Fortune Green and -5% in Highgate.

Two more by-elections are due next week (in Harrow and Brent).