How would PR have changed the face of Parliament?: The Alternative Vote

How it works: MPs are elected from the existing constituencies. Voters number candidates in order of preference. Any candidate who gets over 50 per cent of the vote is automatically elected. If no candidate attains that share, the candidate who came bottom on first preferences is eliminated and his or her second preferences reallocated. This process of elimination continues until a candidate has more than 50 per cent support, or only two are left, in which case the candidate with the most votes wins. (This is the system closest to Supplementary Vote, to be proposed by Plant for Labour.)

For: One of the simplest systems: in the ICM poll, virtually all respondents successfully filled out the ballot paper. Existing constituencies are retained, and the elected MP has the support of a majority of voters.

Against: Apart from the last, the effects of AV are pretty similar to First Past The Post. It is not a proportional system. As can be seen from the table above, Liberal Democrats still come far short of the 18 per cent of the seats they deserve from their national vote. The LSE report comments: 'Even under AV, the Conservatives could well continue to win overall majorities in the Commons at the end of the century, with support no greater than their current minority vote.'

----------------------------------------------------------------------- How it would have changed the Commons ----------------------------------------------------------------------- Con Lab Lib Dem SNP/PC Green MPs 325 (49.9%) 270 (41.5%) 30 (4.6%) 9 (1.4%) 0 -----------------------------------------------------------------------