Number cruncher: Who wins in Commons shake-up?

The coming year could see the biggest change in the way we elect our MPs since women were granted the vote on the same terms as men in 1928. The Parliamentary Voting System and Constituencies Bill proposes cutting the size of the House of Commons from 650 to 600, and holding a referendum in May on whether to switch from first past the post to the alternative vote. Even if people do not vote for AV, then—assuming parliament approves the bill, and it might have problems in the Lords—we still get a smaller Commons.

Suppose that those changes had been in place in last May’s general election: how would the result have differed? The two most thorough analyses have been done by Democratic Audit (for Newsnight) on the change in the number of MPs, and by a team led by David Sanders of Essex University on the impact of AV.

Taking the seats-reduction first: Labour would have lost the most. This is because seats held by Labour tend to have smaller electorates than those held by Conservatives or Liberal Democrats. The new law would make the equalisation of electorates paramount; so the inner cities and industrial areas, with their smaller, left-leaning constituencies, would bear the brunt of the loss of seats.

On the other hand, the alternative vote would have hurt the Conservatives more than Labour—and given the Liberal Democrats a boost. This is because YouGov data for the British Election Study (the basis of the Sanders team’s analysis) shows that more Lib Dem voters would have made Labour their second choice than the Tories, while second-place Lib Dem candidates would have benefitted from the second-choice votes of the local third-placed party, whether Labour or Tory.

Combining the two analyses is inevitably a hazardous exercise; but it looks as if the combined impact of the changes would have left the Tories with around 273 seats (34 fewer than they actually won), Labour with 224 (also 34 fewer) and the Lib Dems with 80 (23 more). This would have created the possibility of a Labour-Lib Dem coalition, with an overall majority of eight.

However, surveys since the election have shown a steady drift towards a “no” majority in the May referendum. The biggest changes have been among Labour voters: in June a narrow majority of them would have backed AV; now the “noes” outnumber the “yeses” by 15 points.

Had there been a smaller Commons last May, but no electoral reform, then not only would a Lib-Lab alliance not have had a majority, its combined strength would have left it 11 seats short of the Conservatives. The chances are, David Cameron would now lead a one-party minority government, not a coalition.