System failure: all voters are equal, but some are more equal than others

Last week's election result seems set to reignite the debate about electoral reform. Labour secured a comfortable majority, 67, despite winning no more than 35 per cent of the vote and a lead of just three points over the Conservatives. Never before in British electoral history has so much power been secured with so few votes.

The outcome would have been very different had the election been held using proportional representation. PR comes in many forms; under one such system, the country is divided into 12 regions, just as it is in European elections, and seats are allocated in accordance with each party's share of the vote in each region. However, we have also assumed a party has to win 5 per cent of the vote in a region before it wins any seats.

With 247 seats, Labour would have 109 fewer MPs than it has now. The Liberal Democrats would have 148, 86 more. The Conservatives, with 217 seats, would be 19 better off. This result is not perfectly proportional. With 38 per cent of the seats, Labour would still have a slight advantage. This is primarily because the 5 per cent threshold stops smaller parties from winning any seats.

But Labour would no longer have a majority. The Liberal Democrats would hold the balance of power. If they entered into a coalition with Labour, the two parties combined would have 395 seats, a majority of 144. If the Liberal Democrats formed a coalition with the Conservatives, the two parties would have 365 seats, a majority of 81. Either way the coalition would be formed by parties that between them won over 50 per cent of the vote. However, critics of proportional representation would argue that the Liberal Democrats would have more than their fair share of power.

There are other systems that might be used. One is the additional member system, whereby some MPs are elected using the current first-past-the-post system, while others are elected from regional lists in such a way that the overall result is more proportional. Variants of this system are already used in Scottish Parliament, Welsh Assembly and London Assembly elections.

So long as around half of all MPs are elected from the lists, the overall outcome would be similar to that of the regional system. But if substantially fewer MPs were elected from the lists, Labour would win more seats, and the Liberal Democrats fewer.

A second possibility is the Single Transferable Vote in constituencies that elect between, say, three and six MPs. Under this system, voters do not just say which candidate they like best, but place the candidates in order of preference. It is already used in Northern Ireland for all elections other than to the House of Commons, and will be used in Scottish local elections from 2007.

Locally popular independents and minor party candidates like George Galloway could win the occasional seat under STV, though overall they would still be under-represented. For the rest, STV places a premium on an ability to pick up the second preferences of other parties' supporters, a feature which at present would be likely to benefit Labour and the Liberal Democrats, but would hurt the Conservatives.

The willingness of Labour and Liberal Democrat voters to support each other's candidates may help to explain why some in the Labour Party, including Peter Hain, favour a variant of STV known as the Alternative Vote. Under this system, voters still rank the candidates in order of preference, but only one MP is elected in each constituency. This would have produced an even more disproportional result, a Labour majority of 98.

Not all demands for change are for more proportionality.

John Curtice is Professor of Politics, Strathclyde University

Speaking PR...

Tony Blair

"We are committed to a referendum on the voting system. An independent commission on voting will ... recommend a proportional alternative to the first-past-the-post system." - 1997 MANIFESTO

Lord Patten

"This system is bad for government; it produces these crazy majorities, which aren't good for the Prime Minister and the Cabinet, let alone anybody else."

Lord Kinnock

'It is not really defensible that in a relatively few constituencies, by literally dozens or scores of votes, the direction of the country's policy should be decided.'

Charles Kennedy

'The case for PR has never looked so strong. It's high time the Government extended fair votes to Westminster. It would give us a system which made every vote count.'

Vernon Bogdanor

'The argument that PR leads to coalitions is weak. We have seen elsewhere that when a population wants a single party government, they vote for it.'