John Curtice: You may be bored, but we need all this madness

For four endless weeks, politicians rudely disturb the routine of our night's viewing on the sofa

It seems to be nothing but madness. Party leaders zig-zag across the country in helicopters with barely time to say hello to anyone before they are off in the air again. They give lengthy press conferences before anyone has had time to have breakfast. Meanwhile, for four endless weeks the fruits of their daily labours rudely disturb the regular routine of our night's viewing on the sofa. Can any of this really persuade us how to vote? Do we not already know who will win on 5 May, anyway?

It seems to be nothing but madness. Party leaders zig-zag across the country in helicopters with barely time to say hello to anyone before they are off in the air again. They give lengthy press conferences before anyone has had time to have breakfast. Meanwhile, for four endless weeks the fruits of their daily labours rudely disturb the regular routine of our night's viewing on the sofa. Can any of this really persuade us how to vote? Do we not already know who will win on 5 May, anyway?

Mad and disruptive they might be, but in truth we need our election campaigns. We do not all of us know how we are going to vote, and the decisions we make over the next three weeks could yet make a difference to the political direction of the country.

Even in the 1950s, when every voter was supposedly either determinedly Labour or staunchly Conservative, election campaigns still made a difference. At that time some of the first research ever to be conducted into just how we vote found that no less than one in four either changed or made up their minds during an election campaign. In much the same way, just this week at least one in 10 have been admitting to the pollsters they do not know how they are going to vote, while even among those who think they do know how they will vote around one in three say they might still change their minds.

Moreover, this campaign churning is often crucial to the fortunes of one of our political parties: the Liberal Democrats. In most post-war election campaigns support for the country's third force has ended up being higher on polling day than it was at the outset of the campaign. In 1997, for example, the Liberal Democrat vote increased by 3 points, while last time around in 2001 it increased by no less than 5 points.

There is probably one simple reason why election campaigns matter so much to the Liberal Democrats: it is pretty much the only time that anybody gets to hear anything about them. Outside elections they have to compete for airtime, and often get squeezed out. But during election campaigns the broadcasters have to give them a guaranteed amount of coverage, even if what they have to say does not appear to be newsworthy at all.

Of course not all publicity is good publicity, as Charles Kennedy learnt to his cost this week when his sleep-deprived brain got into a muddle about local income tax. In 1987, when the former Liberal/SDP Alliance was being jointly led by David Steel and David Owen, the media often used the Alliance's airtime to report on how the two Davids appeared to have two rather different campaign messages. But usually the greater attention they receive at campaign time seems to do the Liberal Democrats good.

Britain's two largest parties cannot afford to relax either - if only to ensure that they do not lose more ground to the Liberal Democrats than do their principal opponents. After all, Labour's average poll ratings fell by 5 points in each of the last two election campaigns, something the party can ill afford to let happen this time around. Occasionally, if only very occasionally, movements during the election campaign can even actually make a difference to who wins. Mr Heath's unexpected victory over Mr Wilson in 1970 is the most famous example.

In any event, election campaigns are not just about who wins and who loses. They also serve other vital roles. For a start, they create a kind of informal contract between the Government and the governed. The victors are expected to keep the promises they have made in their campaign, and woe betide the party that is felt not to have done so - as Labour has found to its cost over both its decision to introduce top-up fees and its 1p hike in national insurance.

Election campaigns are also a kind of job interview. Prospective prime ministers have to be able to defend their plans against the scrutiny of both the press and their opponents. If they do not look up to the job, on polling day they are served with a rejection letter.

Meanwhile, for all our complaints about just how boring and uninteresting election campaigns are, in practice they actually make us feel better about how we are governed. Once it is all over we are always more inclined than we were beforehand to say that politicians can be trusted to put the country's interests above the interests of their own party. Perhaps we feel their hearts must be in the right place after all if they are willing to spend four incessant weeks engaged in such tireless and tiresome activity. Why else would they possibly bother?

John Curtice is Professor of Politics, Strathclyde University