If there was a central theme of British political history in the first half of the 20th century, it was the rise of the Labour Party; the theme of the second half looked very much like its decline and fall. After the high-water mark of the 1945-51 government, the party held office for only 11 out of the next 46 years, and by 1992, when the Tories won a fourth consecutive election, it was possible to think that Labour was finished, like the Liberals before it. Then came a miraculous recovery, an election landslide followed by two more victories; so that, by early November this year, Labour will have been in office for twice as long as the Attlee government.

And yet it has all turned to ashes. The government today is in office but not in power; a ministry of the living dead. Most of the blame is now heaped on Gordon Brown. Many people who once acclaimed him as hero and saviour have savagely turned against him, and it's true that he has bungled one problem after another - from Northern Rock and the election-that-wasn't to Lockerbie and the cuts-that-aren't-cuts.

All this might seem to leave Brown's predecessor looking much better. But could it be that Tony Blair, ostensibly Labour's most successful leader ever, succeeded at the cost of morally eviscerating the party and inflicting the kind of damage from which it will never recover? Blair likes to say "history will be my judge". Maybe history will judge him as the man who destroyed the Labour Party - but with the party a willing accomplice. In the past, Labour had excuses for failure; this time it is ­dying by its own hand.

It began life as just that - the party of labour, the political voice of the organised working class. As its first leader, Keir Hardie, said in 1903: "When acting in the House of Commons, they should be neither socialists, Liberals, not Tories, but a Labour party." In 1918, inspired by Sidney Webb, one of the first Fabians and a founder of the New Statesman, Labour adopted its first socialist programme. Webb preached "the inevitability of gradualness", and in 1923 predicted that, "from the rising curve of Labour votes", the party would obtain a clear majority "somewhere about 1926".

Creed of injustice

Although that didn't happen, Labour formed two governments in that decade. In January 1924, George V sent for Ramsay MacDonald, the Labour leader, observing as he did so, "Today, 23 years ago, dear Grandmama died. I wonder what she would have thought of a Labour government!" Whatever Victoria would have thought, that government lasted less than a year before it fell and was routed at the polls following the scandal of the "Zinoviev letter", which purported to be written by the head of the Comintern and scared voters over to the Conservative Party.

In 1929, Labour and MacDonald were back, but only until the financial crisis in the summer of 1931, when MacDonald became prime minister in a national government that implemented savage cuts, before an election at which Labour was crushed.

Those first two minority Labour governments could introduce few drastic reforms, although they achieved more than is often remembered, from Wheatley's Housing Act of 1924 to the Coal Mines Act 1930 and Greenwood's slum-clearance programme. And they both came to grief in a way that fuelled a Labour creed of injustice: "We was robbed." Or rather, in the first case, "We were cheated", and in the second, "We were betrayed". But in turn that meant: "We can recover."

In 1945, they did. After an electoral landslide in which Labour came close to an absolute majority of votes, the party embarked on a hugely ambitious programme. Labour won another election in 1950 with a slender but manageable majority, but Clement Attlee was bullied by George VI into calling an election in October 1951, and lost. "We was robbed" again, this time by the voting system, which gave the Tories more seats even though Labour had won a clear majority of the popular vote. Indeed, at almost 14 million, the 1951 Labour vote was the largest the party has ever achieved.

Despite its sorry end, the Attlee government had transformed the country in a way no Labour government had before - or has since. And so the party could still claim an identity, and purpose: "The Labour Party is a moral crusade or it is nothing," as Harold Wilson put it, albeit not very convincingly. Although he won two elections, in 1964 and 1966, no one can call his government much of a success. It proved incapable of dealing with underlying economic and industrial problems, and staggered from one crisis to another.

But at least it ended the death penalty and allowed the liberal reforms on homosexuality, divorce and abortion passed while Roy Jenkins was home secretary, besides Wilson's one good deed in keeping us out of the Vietnam war. When he returned to office in 1974, the party was as fractious as ever and economic crises multiplied. After Wilson was succeeded by James Callaghan, the story grew more woeful still, ending with the defeat of the government in the Commons in 1979 and Margaret Thatcher's victory.

For much of the next 18 years of opposition, Labour seemed in an almost terminal condition. At the 1983 election, it won 28 per cent of the popular vote, a lower proportion than at any election since 1918. That was followed by a third defeat and a fourth. And then came Blair. Under him, Labour became electable once again and even, so the story runs, a natural party of government, which won three election victories. That is the legacy supposedly squandered by Brown.

But is it as simple as that? For one thing, those victories are less impressive the closer you look. In 1997, Labour won a landslide - of parliamentary seats, that is, roughly 64 per cent of them, but with only 43 per cent of the vote. In the exultation of that moment, not enough Labour supporters noticed that their party had won fewer popular votes than had the Tories under the much-mocked John Major in 1992. In 2001, Labour won again, and not very surprisingly: the electorate by now had a choice between William Hague, a conservative who couldn't win, and Blair, a conservative who could, and did the logical thing, though millions followed another logic by simply not voting.

Morally ruined

The British were once enthusiastic voters, as other nations still are: the 84 per cent turnout at our 1950 election was matched in the latest French presidential election and Dutch general election. In the UK, in 1997, the figure fell to 71 per cent, but then plummeted to 59 per cent in 2001. If fewer people voted Labour in 1997 than Tory in 1992, then fewer voted Labour in 2001 than Labour in 1992; and fewer voted Labour in 2005 than for the Tories at their debacle of 1997.

By that last election, the 35 per cent of the electorate who voted for Labour as the "winning" party was for the first time easily outstripped by those who didn't vote at all. Over the past three elections, the Labour vote has fallen from 13.5 million to 10.7 million to 9.6 million; the last figure is several millions smaller than those who voted Labour when the Tories won in 1959 or 1970 or 1979. Blair gained his victories by default. Should the party really thank him for that?

Some really did believe in 1997 that Blair would bring a new dawn of radical reform. Leave aside ridiculous agitprop from those times such as The Blair Revolution by Peter Mandelson and The Unfinished Revolution by Philip Gould. Much more revealing about the delusions of 12 years ago is Will Hutton's The State to Come, a true period piece, published just before the 1997 election, in which he argued that "only a future Labour government will be able to set a new agenda for Britain".We were witnessing "the strange rebirth of liberal England", Hutton wrote, insisting that the Blair government would raise income tax, redistribute wealth and strengthen the trade unions. And it was a particular article of faith for Hutton and others like him that, once Blair was elected, we would join the single European currency as soon as possible.

It's tempting to say that if Hutton really did believe that, then, like Rick going to Casablanca for the waters, he was misinformed. But was there any honest excuse? To be fair, it wasn't then easy to imagine that before he left office Blair would be plausibly described as standing to the right of every postwar prime minister apart from his lodestar, Margaret Thatcher. Nor could we have guessed that he would take us into a needless and criminal war by means of blatant deception in order to demonstrate his loyalty to the most reactionary American president of modern times.

All the same, the moral and intellectual vacuity of the "New Labour agenda" was easily visible from the beginning, at least to some of us who weren't starry-eyed. I wrote an essay on Blair for the Atlantic Monthly in July 1996 in which I pointed out that: "He is the first of the Tories' political opponents ever to concede that they have largely won the argument . . . An anthology of Blair's recent reflections speaks for itself. 'I believe Margaret Thatcher's emphasis on enterprise was right.' 'Duty is the cornerstone of a decent society.' 'Britain needs more successful people who can become rich by success through the money they earn.'"

Someone else who saw the implications of this was the veteran political commentator Alan Watkins, who put it wittily well before Blair won his first election. On the Lions tour of New Zealand in 1971, their coach, Carwyn James, had told his team to "Get your retaliation in first". All Labour prime ministers had disillusioned their supporters once in office, Watkins wrote, but Blair was unique: he had got his disillusionment in first. And Watkins also saw that although Labour MPs had gone along with Blair in the hope of winning after so many years of defeat, most of them hated what he was doing to their party. They hated it more and more with every year, but he was winning. Those MPs were not deceived by him, they deceived themselves, and they were morally ruined in the process. This time, Labour had no excuses.

A poisonous legacy

Although Blair did not "destroy socialism", as some fervent right-wing admirers have claimed, he did destroy two older traditions that had long nourished Labour: liberal and radical. Any idea of "the strange rebirth of liberal England" rings bitterly hollow after years of relentless assault on civil liberties and the rule of law by a prime minister who sneered at "libertarian nonsense". And the old radical tradition of "the party of peace" died in March 2003, when a majority of Labour MPs voted for an illegal war in which most of them didn't believe. Still, they had their flat-screen televisions and champagne flutes, even if they couldn't all look forward to a $10m annual sinecure from a Wall Street bank like Blair himself.

Therein lies Blair's poisonous legacy. From Baldwin to Thatcher, there was always that healing myth of injustice with which Labour could console itself. This time Labour knew what Blair was doing, and how the party's entire heritage had been contemptuously abandoned. Today there can be no cry of treachery. This time Labour wasn't betrayed by false friends or tricked by bankers: it betrayed and tricked itself. Even if they wanted to, Labour MPs could scarcely any longer sing "Let cowards flinch and traitors sneer, We'll keep the Red Flag flying here", since they themselves are the "cowards and traitors".

Although it may be correctly said that this is not written "from the left", I was, as it happens, brought up in the bosom of the Labour Party (that was just as possible in progressive-professional north London as in a Welsh ­mining village), before I rejected socialism intellectually. But those who have lost a faith often feel a wistful fondness. Former Roman Catholics can retain a respect for the church, or at least for its cultural residue, and certainly warmth towards individual priests and nuns. In the same way, without any longer accepting the party's original beliefs, it was possible to feel a real affection for the Labour Party and for Labour people - old Labour, that is.

Did anyone ever feel any affection at all for the party led by Blair? No normal person could like the junta of Blair, Gould, Mandelson and Campbell. They might have inspired awe, or plain fear, as long as they were winning. But now that it is disintegrating, New Labour has no reserves of love or loyalty to draw on. Sincere believers can inspire respect even when they are losing; once cynical apparatchiks and careerists lose power, they inspire nothing but contempt. Maybe the story of our times will be the death of Labour.

Geoffrey Wheatcroft's books include "The Strange Death of Tory England" and "Yo, Blair!".