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Parliamentary elections in the United Kingdom should be seen as a referendum on the performance of sitting MPs, not merely as a snapshot nationwide opinion poll determining party voting weights for the next Parliament. The electoral system affects the degree to which voters may hold their representatives to account for their actions in the previous Parliament; changes which would diminish this accountability mechanism should be resisted.
The UK presently has a legislature whose unelected chamber better reflects the relative strength of the Labour, Conservative, Liberal Democrat and None of the Above parties. Conversely, if Labour and the Conservatives each won 50% of the vote, the other chamber would have a sizable Labour majority. 51% of the seats in the Lower House delivers 100% of the power, and this can be captured by Labour on about 40% of the vote. Nevertheless, whenever Labour runs into opposition from the chamber which, in any other context, would be described as more "representative" by people who go in for that kind of thing, it threatens to force its legislation through under the Parliament Acts, on the grounds that the Lower House is more "democratic".
The Lower House is more democratic.
Contrary to the self-serving views of the Liberal Democrats and other jejune supporters of electoral "reform", what matters for democracy is not representativeness or proportionality, so much as accountability and responsiveness. When MPs behave in accordance with their constituents' wishes, this is to be preferred to their merely existing in party groupings of such sizes as best reflect their constituents' choices at the previous election.
When discussing electoral reform in the UK, retaining a "constituency link" is often posited as a requirement. That is to say, it is felt to be necessary that everyone should have an MP who is in some sense "theirs", normally meaning that people are grouped into geographical areas and each area gets its own MP. A weaker version of this permits multiple MPs for each area. This is supposed to be good because it means that there's automatically someone in Parliament to go to with one's grievances. There is a much better reason why it happens to be good.
If we merely say that everyone must have one or a small number of MPs, that does not imply that every MP must have his own constituency. The German federal electoral system and its antipodean imitator in New Zealand affords MPs who have no constituencies: they are elected from party lists and assigned in such numbers as ensure that the proportion of MPs in each party in the chamber match the proportion of the vote each party won. This category of MPs shares the same vice as MPs in a chamber fully elected by a proportional system: they can't be voted out of office directly.
If your MP decides to go against the wishes of his constituents, they can contact him and say, "Hi, your majority at the last election was 2000; we, the undersigned 1001 who voted for you last time will vote against your party next time unless you buck the whip on this issue we care about." The easier it is to do this, the more likely the behaviour of an MP will reflect the wishes of constituents.
Don't believe the canard about votes not counting: every vote against the person who won counts against his majority and makes him more susceptible to pressure from his constituents before the next election.
The electoral system can restrain this tactic. It works well under First Past The Post, and similar systems. Generally, increasing the number of MPs who represent a single constituency has the effect of making this tactic harder, as the punishment from electors may be spread across several MPs, especially if the electors cannot choose which MPs from a paricular party get the benefit of their vote. This is a notorious problem with the European Parliamentary elections in Great Britain: if some MEP is the ringleader for a particularly odious policy, she cannot easily be voted out without voting out the colleagues from her party. Even when a free choice on the preferential ordering of MPs is permitted, it is difficult to stop the disliked MP from riding back to election on the coattails of his more popular colleagues.
So, in order of preferability, the electoral systems rank as follows:
- First Past The Post, and Alternative Vote
- Single Transferable Vote in multimember constituencies
- Proper Proportional Representation systems with open lists
- Proper Proportional Representation systems with closed lists
Alternative Vote is the Australian name for a system which when used in single-member constituencies is identical to STV: electors rank the candidates in order of preference, and the least popular candidate is repeatedly eliminated until someone has over 50%; essentially, once a candidate is eliminated, a vote is regarded as counting for whichever remaining candidate was most preferred by its caster. The effect of this system tends to be obliteration of extremists without penalising or "wasting" protest votes.
It should be noted that in the British debate, "Proportional Representation" is used to mean proper PR systems and STV/AV. The Australian Electoral Commission used to have an excellent webpage with a classification of all the electoral systems used in Australia's twenty-odd legislative chambers, but they've apparently improved it off their site now.
Other fallacious views on electoral systems which it is useful to rebut at this juncture include the contention that FPTP entrenches a two-party system (in fact, the number of parties is contingent on the geographical concentration of voters), that AV in the UK in 1997 would have led to a larger Labour majority (only if you didn't tell people and the parties what the electoral system was in advance, otherwise the parties would have behaved differently), and that geographical constituencies are a relic of a bygone age and are being replaced by PR across Europe, or at least the world. FPP is described by Hilaire Barnett in her militantly Anglosceptic tome on the British constitution as "still" existing in some dusty English-speaking corners of the planet; in fact some countries using PR have been moving towards constituencies: Italy did in the 1990s, and the Dutch are considering a similar move.