As Mike Smithson helpfully points out today on PoliticalBetting.com, while there is a small difference in the size of electorate between Conservative-held and Labour-held seats, there is a much bigger difference in the average turnout:
The average level in CON seats was 68.4% while in LAB seats it was 61.1%. It is this gap which is behind much of the distortion.
In Labour’s heartlands, where the outcome is not in doubt, far fewer people bother to vote. This is not something you can change with legislation.
Unless there’s a drastic change in voting patterns, which I very much doubt, there will still be a much higher vote threshold for the Tories to win an overall majority than Labour however much you bring average seat sizes into line.A higher turnout (or even compulsory voting) wouldn’t solve this problem either. All it would do is pile up bigger majorities for Labour in its safe seats.
If Cameron wants to redress the balance, his only hope is proportional representation – and we already know what he thinks about that.