THE day after tomorrow, it will be 100 years precisely since what was probably the greatest electoral victory in British parliamentary history. The Liberals, led by the canny Glaswegian Henry Campbell-Bannerman, routed the Tories in a spectacular landslide. The Tories' strength in the Commons fell from 402 in 1900 to just 157. And they were utterly wiped out in Wales, the territory of the greatest Liberal of them all, Lloyd George.

Yet could the Liberals capitalise on this momentous victory? They could not. For a hundred years the party has been in steady and, for the most part, pitiful decline, to the extent that it is now largely a forlorn depository for nice, decent losers (although niceness and decency have not been very evident in recent days).

Many have tried to analyse what went wrong after that stunning success 100 years ago. Probably the main reason was that the Liberals could not respond to the growth of the trades unions. The links between the nascent Labour Party and the unions were the key to the rapid growth of Labour, which eventually all but eclipsed the Liberal Party.

Winston Churchill, the greatest parliamentarian of the previous century, and a man who was a pragmatist as well as a romantic, boasted in 1910: "I am an English Liberal. I hate the Tory party." Forty years later, this early master of the soundbite had changed his tune. He summed up the Liberals in five cruel but pertinent words: "So few, and so futile."

Futility has indeed been the watchword. The Liberals were down to five MPs in the 1950s, their nadir; and while there have been revivals and flurries since, they have never been close to grasping power. In the most recent general election they gained 62 seats, which some said was a good result. Hardly; it just adumbrated another four or five years of futility.

The Liberals had articulated an honourable and consistent opposition to the disgraceful war in Iraq, but were unable to capitalise electorally on this against a weak Tory party that supported the war. There was vainglorious talk of "decapitating" leading Tories such as David Davis, but this turned out to be so much hot air.

For several generations, the Liberals have languished as the third party in what remains essentially a two-party system. The way to change that would obviously be through electoral reform. Once or twice the Liberals have had a chance to exercise leverage to persuade either of the main parties to consider electoral reform.

The best opportunity came in the first general election of 1974 when the prime minister, Ted Heath, narrowly lost to Harold Wilson in terms of seats (297 to 301) though his Tories actually won more votes. Heath, as he had the constitutional right to do, refused to concede to Wilson in the aftermath of the count and, after two days of brooding, he approached Jeremy Thorpe, then the Liberal leader.

The Liberals had only 14 seats but Heath proposed a deal. The key offerwas a major Speaker's Conference on electoral reform, to be followed by a free vote in the Commons. This was not as much as most Liberals wanted, but it was still a remarkable offer. Had Thorpe seized the moment, he might just have changed British political history.

Heath also offered Thorpe a seat in the cabinet. The cabinet secretary advised Heath not to give Thorpe the job of home secretary because of issues in his private life (no doubt this was a reference to Thorpe's violent homosexual relationship with Norman Scott). But the one post that Thorpe really coveted was that of home secretary. Thorpe dithered, and the opportunity was lost.

Three years later, the Liberals formed a pact with Labour, and effectively shored up Jim Callaghan's failing government for 18 months. Although Callaghan and the Liberal leader, David Steel, had a reasonable working arrangement, the relations between their two respective strong men, Denis Healey and John Pardoe, were combustible if not downright contemptuous, and the Liberals never gained any meaningful return for supporting an ailing administration.

It is thus difficult to discern why the Liberals exist, at UK level. They have been on the far margins of power for so long that when they have even a whiff of it they seem to panic. Their record in local government has been effective, and in Scotland they have made a useful contribution to the f ledgling parliament, through their coalition with Labour. But, in UK terms, they have been a joke. Sixty-two MPs is obviously many more than five, but it is still a very long way from an effective base on which to prepare for government.

The best the Liberals can hope for is a hung parliament in the 2009 or 2010 general election. That would give them, once again, the opportunity to exercise leverage.

But would a party led by Sir Ming Campbell, by then nearly 70, have the nerve or the skill to do so? Politics is about power, its pursuit and exercise, and the Liberals have been bereft of power for so long that they have become a sad and desolate irrelevance.