Leading article: The big trade unions show their regressive side

The referendum on changes to the electoral system is shaping up to be the political event of next year. As it should be. Voting is a serious matter, and no alteration to the established way of doing things should be undertaken lightly or without exhaustive discussion. While not as fundamental a reform as The Independent and other advocates of proportional representation would like, a move to the Alternative Vote system would still be a landmark change for a country that has used first-past-the-post since modern elections began.

The battle lines are already being drawn up. Late last month, the "no" campaign introduced its leaders: Margaret Beckett was named president; David Blunkett and Lord Prescott were given supporting roles, along with the Foreign Secretary, William Hague, and the Justice Secretary, Ken Clarke, making it a truly crossbench affair.

Two weeks later, Labour's "yes" campaign started to declare its hand, with an appeal to party members from shadow ministers and others, resembling New Labour in exile. Headed by Ben Bradshaw and Alan Johnson, the signatories included Douglas Alexander, John Denham and Tessa Jowell, and Lords Adonis and Mandelson, but also "characters", such as Ken Livingstone and Tony Benn.

Now a new dimension has been added, with the disclosure that the country's two biggest trade unions, Unite and the GMB, are to join forces with the "no" campaign. While undoubtedly adding fire-power to the opponents of reform, this union support holds out the tantalising prospect of a very odd couple indeed making common cause. Die-hard supporters of worker-power and representatives of the Conservative squirearchy could find themselves on the same side, extolling the advantages of first-past-the-post. And their hostility to change stems from the very same self-interest: the potential threat AV represents in constituencies that have essentially been one-party fiefdoms for decades.

Which raises two questions. The first concerns the propriety of trade unions lining up behind one campaign or other. As the lists of MPs who have already declared their allegiance shows, the two biggest political parties are divided on the merits of change, which is a healthy sign and bespeaks an energetic and keenly fought campaign. A referendum is the national equivalent of a parliamentary free vote and a rare opportunity in British politics. Should trade unions be permitted to use their resources to influence opinion one way or another?

The second question relates more directly to vested interests. AV is not PR, and would not transform British politics in the way PR, in one or other of its forms, might have done. Taken together with boundary changes, however, it would nonetheless shake up politics, probably to the detriment of Labour. So the motives of sitting MPs need to be examined. Is it really the high principle of electoral practice that motivates them or the rather less elevated desire to hang on to a safe seat?

The preliminary supporters' lists, on either side, show that those who oppose a switch to AV are, by and large, small-c conservatives and politicians, to a greater or lesser degree, rooted in the past. That alone should send the clear message about where the future of the UK electoral system lies. There will be trepidation, to be sure. But anyone who fears a step into the unknown should find reassurance in the changes that have taken place in recent years. Since devolution, Scottish, Welsh and Northern Irish voters have all coped successfully with mixed electoral systems, and voting for the European Parliament takes place according to party lists. Contrary to widespread belief, the UK is not incapable of electoral change. It is for the "yes" campaign to make its case.