How would PR have changed the face of Parliament?: The Additional Member system

How it works: This system has two different types of MP; those elected under the First Past The Post system, and additional 'top-up' members chosen from regional lists to bring a party's seats in the region into line with the proportion of votes gained. It is generally suggested that a threshold of 5 per cent of the vote should be imposed before a party is allowed any top-up seats. In the referendum held last year in New Zealand on electoral reform, this was the system preferred, by 64.6 per cent, a wide margin.

For: This and other list systems can be called the fairest, in that they guarantee an equal percentage of votes and seats. The voting system is relatively simple - see ballot paper. It is in essence the system that applies in Germany, and there, at least, has ensured stable coalitions.

Against: Detractors claim that two classes of MP would be created - one tied to a constituency and the workload that would result from that, the other freer to pursue fame and glory. The old constituencies would probably be replaced with ones twice the size. Much debate has gone on over the best split between 'local' and 'top-up' MPs: the Hansard commission in 1975 suggested 75 per cent to 25 per cent, but 50/50 is more popular and would be more likely to result in proportionality.

---------------------------------------------------------------------- How it would have changed the Commons ---------------------------------------------------------------------- Con Lab Lib Dem SNP/PC Green MPs 268 (41.2%) 232 (35.6%) 116 (17.8%) 18 (2.8%) 0 ----------------------------------------------------------------------