As any sports star will testify, change the rules and you change the way the game is played. Defenders and strikers would apply new tactics were soccer's offside rule to be amended. Bring in a new leg-before-wicket law, and bowlers and batsmen would act differently.
Politics is the same. Change the voting system and you change the way parties fight elections and voters decide whom to support. We can't simply read across from the size of each party's vote at the last election and "rerun" last year's general election under different systems on the basis that Labour, the Tories and the Lib Dems would still have won 36 per cent, 33 per cent and 23 per cent of the vote respectively.
Nor should we rely too heavily on some imaginative polling work that has been done after recent elections to ask voters what they would do under different systems. These cannot capture the dynamics of party campaigning and the way voters gradually adapt to the new rules. In elections to Scotland's parliament, support for the minor parties more than doubled, from 10 per cent to 22 per cent, between the first contest in 1999 and the second in 2003. In 2004's UK-wide European parliament elections, the second to be fought under proportional representation rules, the combined Labour and Conservative vote fell below 50 per cent.
What, then, would happen at Westminster were the voting system to change? We cannot, of course, be certain; but we can look at the influences that would come into play under different systems, and make some educated guesses about their impact.
Alternative vote (AV)
This is the most modest change. Each MP would continue to represent a single constituency. But instead of marking their ballot papers with an "X", voters would list their candidates in order of preference: 1, 2, 3 and so on. If no candidate won a majority of first-preference votes, the least popular candidates would be eliminated, and their supporters' second and, if necessary, subsequent preferences would come into play, until a candidate reached the 50 per cent mark. These are the probable consequences of AV:
Single-party majority governments remain likely.
The Liberal Democrats would win more seats, by attracting a significant share of the second preferences of Labour and Conservative voters, where their own party’s candidate runs third.
The main losers are likely to be the less popular of the two main parties. Under AV, the Conservatives may have won even fewer seats in 1997, and Labour even more seats. This is because the AV system intensifies the power of negative voting, by allowing voters to use their preferences to keep out candidates (and therefore parties) they really don’t like.
The main parties would have to consider some kind of relationship with the Lib Dems, in order to benefit most from the preference system. After all, both Labour and the Conservatives would be competing for the second preferences of Lib Dem supporters in Lab-Con marginals. Some kind of reciprocal second-preference recommendation between, say, Labour and the Lib Dems, could help both parties.
Extremist parties, such as the BNP, would find it much harder to win seats in councils or at Westminster if councillors and MPs were elected under AV. In 1998, the Australian right-wing nationalist Pauline Hanson fought the Queensland constituency of Blair, and received 36 per cent of first preference votes, well ahead of the 21 per cent garnered by her nearest rival. Under first-past-the-post, she would have won. But under Australia’s AV system, second and third preferences were then counted; she failed to advance much beyond her 36 per cent core vote and lost.
Non-extreme small parties would not be at quite such a disadvantage, but the odds would still be stacked against them. The Greens would still find it very hard to elect an MP to the Commons.
Additional Member System (AMS)
This is the system used for elections to the Scottish Parliament and the Welsh and London Assemblies. Each elector has two votes: one for their local, directly-elected, first-past-the-post representative; the second for their preferred party list for the region. The regional votes determine the overall complexion of each body. If, say, the Purple Party is entitled to 20 seats by virtue of its regional vote, and its candidates win 12 local seats, then eight of its regional candidates will be elected to ensure the correct overall total. Normally under AMS, a party must win 5 per cent of the total vote to qualify for any regional seats.
Here are the likely consequences of AMS:
The main parties will suffer – as we have already seen in Scotland and London.
The Liberal Democrats could see some of their support flaking away to smaller parties such as the Greens and Respect. But while their vote falls, their number of seats could rise substantially – say to around 100 on a 15 per cent vote share.
Small parties stand a chance of breaking through. Both Respect and the BNP came very close to winning seats in the London Assembly in 2004: they fell just short of the 5 per cent threshold. As soon as a party crosses the 5 per cent line in an AMS general election, it becomes entitled to 32 MPs. Suppose the choice were: a) 32 Green MPs and 32 BNP MPs; or b) none from either party – which would you prefer?
Coalitions become almost inevitable (again, as we have seen in Scotland). Over time, the proliferation of parties could mean that the only viable coalitions at Westminster are either "grand" coalitions between the two main parties (as Germany now has), or coalitions of at least three parties – if, say, both Labour and the Conservatives fall below 30 per cent and the Lib Dems below 20 per cent. This might be seen as a desirable, intensely democratic prospect or a fate to be avoided at all costs? Take your pick.
Single Transferable Vote (STV)
The UK would be divided into around 150 large multi-member constituencies, each of which would elect up to five MPs. Electors would list their candidates in order of preference. They would not decide in which order to put the parties, but in which order to put the candidates of their preferred party. The likely consequences are:
Labour and the Tories are both likely to suffer, and the Lib Dems to benefit. Unless their vote collapses, the Lib Dems could expect to win at least one seat in most of the 150 new constituencies.
Smaller parties will have difficulty breaking through. This is because the threshold in each constituency will be around 13-15 per cent (depending on the precise configuration of votes). The Greens, Respect and BNP might win a seat here or there, but not the 30-plus seats they might each be able to win under AMS, if they could pass the 5 per cent mark. (In Scotland, the success of the Greens and Scottish Socialists in 2003 prompted some senior figures in the Scottish Labour Party to regret that they had plumped for AMS rather than STV in the first place. STV would probably have kept out the interlopers.)
Coalition governments at Westminster become much more likely. However, as long as there are only three parties of any size represented in the House of Commons, the Lib Dems will enjoy the semi-permanent role of deciding which party leader, Labour or Conservative, to make prime minister. Only a dramatic election result, or a grand coalition, could deprive the Lib Dems of this power.
"All politics is local" – this would be truer more than ever under STV, as each candidate would be fighting not just against other parties but against other candidates from their own party. In Ireland, which enjoys or endures STV, members of the Irish Dail tend to devote more time than their British counterparts to local, log-rolling, pork-barrel issues, and less to big national concerns. According to taste, this would be either an advance or setback for voter-choice and representative democracy.
As this brief inspection of different voting systems suggests, there is no perfect way of organising national politics. Every system has its advantages and pitfalls. First-past-the-post is unfair to small parties, and allows Labour to govern today with a clear majority in the House of Commons despite winning well under 40 per cent of the popular vote. Many people will deplore the fact that first past the post keeps out the Greens - and celebrate the fact that, for the very same reason, it has kept the BNP out of Westminster (though not local councils).
In short, choosing a voting system is not a quest for perfection. It is arguably not even a quest for the best system, but the one with the least disadvantages.
But whichever is chosen, one over-arching point remains. Look round the world, and lively democracies tend to have one thing in common, whatever electoral system they employ. They tend to produce two main blocs - either parties or coalitions of parties: one in power, the other able to replace it if enough voters get fed up.
When that two-bloc system breaks down, you get a sustained period in which only one party can in practice run the country (as in Italy and Japan for much of the post-war period, or Canada for a decade from the mid-1990s), or grand coalitions are formed (as in both Germany and Austria from time to time). Neither is satisfactory, for both deprive the electorate of the most basic choice of all - which of the principal contenders should run the country.
Different electoral systems can tilt a country towards or away from two-bloc politics; but they cannot stem a strong tide that runs towards single-party domination, two-way choice, or multi-party fragmentation. Britain these days is showing signs of party fragmentation. First-past-the-post is impeding that process at Westminster. For that very reason, some people want to keep FPTP, in order to preserve the efficient choice of government, while others want to replace it, on the grounds that democracy is ill-served when significant minority voices are not properly represented at Westminster.
In the end, there is no perfect solution to this dispute. Each of us must decide what is the main purpose of parties and elections. Our collective decision might well differ from assembly to assembly, and from era to era. Oh, and for readers of the New Statesman, whether they want Labour to survive as the dominant party of the centre-left, despite its mounting unpopularity and dwindling membership, or the Left and centre of British politics to undergo a seismic upheaval.
Peter Kellner is chairman of YouGov
Alternative voting systems
This would be the most modest change in system. Under it single-party majority governments remain likely.
System used for elections to Scottish parliament and Welsh Assembly. Extremists could be let in.
UK to be divided into 150 large multi-member constituencies. Labour and Tories likely to suffer, while Lib Dems would benefit.