IMAGINE if the rules of football were changed so that the goals were doubled in size and you gained extra points for near misses. Big changes in the rules governing electoral systems have an equally dramatic effect on the game of politics, which perhaps explains why they are so rare. Though New Zealand recently moved from the British first-past-the-post system to a form of proportional representation, and Japan and Italy have modified their systems, Arend Lijphart, the leading academic expert on the subject, concludes in his study of 27 countries between 1945 and 1990 (“Electoral Systems and Party Systems”, OUP, £14.99) that “electoral systems tend to be very stable and to resist change.”

But there is now the prospect of just such a change taking place in Britain. While in opposition, the Labour Party signed a deal with the Liberal Democrats. Under it, Labour promised an independent commission to study electoral reform. The commission will recommend a proportional alternative to the existing first-past-the-post system; voters will then be given a choice between the two in a referendum.

Once Labour had won a majority of 179 in the general election, some Labour MPs discovered that the case for electoral reform was rather less compelling than they had previously thought. But there are still many enthusiasts for reform amongst the new, less tribal breed of Labour MPs. The prime minister himself remains “unpersuaded”. But he has kept his promise to the Liberal Democrats nevertheless. On December 1st, he appointed a five-man commission, which has been asked to report within a year.

The commission's terms of reference order it to “observe the requirement for broad proportionality, the need for stable government, an extension of voter choice and the maintenance of a link between MPs and geographical constituencies”, which is a bit like telling it to come up with a way of having your cake and eating it too. As important to its deliberations may be the track record of its members.

Four are declared reformers. Lord Jenkins, the Liberal Democrat who is chairing it, is pro-reform, though there have been hints that he would accept something less than the strongly proportional STV system backed by his party. Lord Alexander, a Tory who is chairman of National Westminster Bank and also one of the trustees of The Economist, announced his “tentative personal preference” for STV in his recent book “The Voice of the People” (Weidenfeld and Nicolson, £17.99).

David Lipsey, political editor of The Economist and author of our “Bagehot” column, has argued in the past for at least the “alternative vote” (AV), generally regarded as a fairly modest reform. (To avoid conflicts of interest, he will take a leave of absence from The Economist during the period the commission is deliberating.) Lady Gould, a former director of organisation for the Labour Party (who is entirely unconnected to The Economist), was a member of a Labour committee chaired by Lord Plant which in 1993 recommended another reform, the supplementary vote—which is even more modest than AV. Only Sir John Chilcot, who retired as permanent under-secretary of the Northern Ireland office on the day the commission was announced, is not on record with a view. However, he has witnessed a proportional system in action in Northern Ireland which uses STV for local elections to make sure both its religious communities are represented.

Even if the commission comes up with a recommendation, change is far from certain. First, the referendum would have to be held; Mr Blair has made no commitment on its timing. Then, there would have to be a vote for change, which reformers might find hard to win if Mr Blair decides that he is still unpersuaded and does not campaign strongly for it. Then legislation would have to go through the Commons. MPs, whose careers depend on the electoral system, cannot be forced to vote for change, even if voters decide they want it.