"Bliss was it in that dawn to be alive, But to be young was very heaven!"

It took a dead British poet to understand May 1968. The conventional French politicians of the time did not have a clue what was going on, even the left-wing politicians. The student and worker revolt in France 40 years ago this spring was a cultural revolution, even a sexual revolution, before it was a political one.

The young William Wordsworth wrote the above lines about a much bloodier French revolution. They express perfectly, all the same, the mood of May 1968: the idealism, the whimsy, the zeal, the humour, the self-righteousness, the excitement.

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The photographs tell the story. On the first night of rioting in the Paris Left Bank, on 3 May 1968, the riot police wore old-fashioned uniforms and old-fashioned helmets. They looked rather like French soldiers from the 1914-18 war.

The male students wore jackets and ties or neat jumpers and short hair and well-pressed trousers. The women had long hair and sensible skirts and hair-bands. There were few jeans or sandals or beards.

This, remember, was more than a year after Sgt Pepper's Lonely Hearts Club Band. It was the year after the Flower Power revolution had begun in San Francisco. No self-respecting, revolting student in America or Britain or Germany would have worn a jacket and tie on a barricade in the first days of May 1968. Before the end of the student revolt in early June, the French students looked more convincingly revolutionary: they were scruffier, more hirsute and more psychedelic. They had lost politically but they had won culturally and maybe even spiritually.

May 1968 was, in its origins, a revolt against the stifling papa-knows-best conservatism, and dullness, of General Charles de Gaulle's economically booming 1960s France. It was, at one level, a catch-up, fast-forward revolution for the right to wear long hair and purple trousers. It began in March, at the new Nanterre University west of Paris, as a demand for the rights of boy and girl students in their late teens and twenties to sleep together.

There were other student revolts in Europe and America, before and after May 1968. In no other country did a student rebellion almost bring down a government. In no other country did a student rebellion lead to a workers' revolt, one that rose up from the blue-collar grass roots and overwhelmed the paternalistic trade-union leadership as much as the paternalistic, conservative government.

The two revolts remained largely separate: despite the efforts of a fringe of Maoist students, despite the eloquence of Jean-Paul Sartre, who stood on a box outside the Renault factory at Boulogne-Billancourt telling the workers about the student-worker-intellectual paradise to come. ("Be brief," someone advised him, but he wasn't.)

The workers' demands were tangible and precise. The students' aims were diffuse and contradictory: more philosophical than political and often shot-through with sexual innuendo (and frustration). "Marxist, Groucho tendency." "Be realistic, ask for the impossible." "Take your desires for realities." "Unbutton your brain as much as your trousers."

Of the two rebellions, it was the wildcat general strike by workers which worried the government most at the time. A young minister called Jacques Chirac was sent secretly to prepare the way for the pay rises, and reduced working hours, which helped to bring the strike to an end. He put a revolver in his inside jacket pocket before going to his clandestine meetings. This was not self-dramatisation; it was just the giddy mood of the times.

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And yet, 40 years on, it is the student revolt which is most remembered and the workers' revolt which has been almost forgotten. This is partly because the leaders of the young people who built barricades and overturned cars in the Paris Latin Quarter in 1968 went on, in many cases, to become senior journalists, writers, philosophers and politicians (including the present foreign minister, Bernard Kouchner).

It is also because the French cultural and sexual revolution of the 1960s was compressed so memorably into four or five weeks. Elsewhere the changes were stealthier. Philip Larkin (another dead British poet) said: "Sex was invented in 1963, between the Chatterley trial and the Beatles' first LP." In truth, the end of the old social and sexual certainties and taboos in Britain was a gradual process from 1963 to 1970, driven by the Profumo scandal, the Beatles, the reforms of the first Harold Wilson government and a virus of revolt carried on the wind of television from Vietnam and the United States.

In France, typically enough, the same transition was acted out in a great, concentrated psycho-drama on the streets. As the French journalist and writer Jacques Julliard said, revolutions in France are "rites of passage". Quiet, peaceful, social transitions, even noisy, peaceful transitions, are not the French Way.

"To go from Louis XVI to Louis XVIII, from moderate absolutism to a parliamentary monarchy, clumsy foreigners would have gone by way of a Louis XVII," M. Julliard wrote. "We went via Robespierre and Napoleon."

By the same logic, France needed six weeks of mayhem to go from grey trousers to purple trousers; from the social and sexual repression of the 1950s to the social and sexual freedom, and confusion, of the 1970s (and afterwards).

The French students who manned the Left Bank barricades thought – among other things – that they were revolting against French-ness itself. In fact, they were behaving in a classically French way.

Perhaps because it was such a French occasion, French commentary to this day tends to treat May 1968 as a purely French phenomenon. Reading some of the French analyses of 1968 – both for and against – one could have the impression that the May student revolt alone created the post-1970s world of tolerance and individualism, free-thinking and consumerism.

Other Western countries were going the same way before France. Most of them had brief or scattered outbreaks of anti-establishment violence in the late 1960s and early 1970s, even of terrorism in the case of Germany and Italy. None of them had a brief, intense, mythologised youth rebellion as France did.

The fast-forwarding of events made the myth of May 1968. And the myth, as myths do, has achieved a life of its own.

During his presidential campaign last year, Nicolas Sarkozy launched into a series of vituperative speeches in which he promised to "liquidate" the legacy of 1968, which he blamed for everything from poor school results to high crime figures and the decline of old-fashioned patriotism.

And yet M. Sarkozy, a twice-divorced, consumerist, value-muddling, politican par excellence, is himself a child of 1968. At least, he is a child of the social changes which 1968 symbolised rather than generated.

Similarly, on the French Left, May 1968, precisely because it was so memorable, has become a sacred totem. Unfortunately, it is the most hidebound, unthinking lefties who cling onto the memory of France's revolution manqué. The open-minded, joyful, jokey, surreal side of May 1968 – the "Groucho tendency" – tends to be forgotten. There are, none the less, specific reasons why "May 1968" – which began in March and ended in June – happened in France in the way that it did.

From 1945 to 1975, still known as "les trentes glorieuses", France enjoyed 30 years of unbroken growth and relative prosperity. After the revolving-door governments and the lost colonial wars of the 1950s, France under President Charles de Gaulle settled into a period of unusual stability in the 1960s (give or take a few incidents of pro-colonial terrorism).

In that period, an old France, mostly agricultural, mostly Catholic, was being quietly buried. In 1945, there were still 7,000,000 farmers and peasants in France. By 1968, there were 3,000,000. (There are now, by the way, only about 500,000.)

The rural population poured into towns and suburbs and worked in offices and factories. Their children thrived in urban schools. Long before 1968, anyone who passed the baccalaureate (equivalent to A levels) had an absolute right to go to university, virtually for free.

In 1938, France had 60,000 university students. In 1961, it had 240,000. By 1968, it had 605,000, as many as Britain, West Germany and Belgium combined. Few new university campuses were built or extended to take the massed ranks of students. Nanterre University was one exception.

Despite the overall rise in prosperity, and levels of education, De Gaulle's France was a quietly oppressive place. Memories of French failure in the war were everywhere but rarely discussed. The general wanted a modern, dynamic France rooted in an old, conservative and non-dynamic social system.

Students felt that they were treated like children and herded like cattle into vast "amphis" or amphiteatres to scribble down notes. Factory workers were treated like inferior beings, by bosses and union bosses alike. They also resented the fact that the 1960s prosperity had failed to trickle down to the shop floor.

In a celebrated, prophetic, but also obtuse, article in Le Monde on 15 March 1968, Pierre Viansson-Ponté said that France was suffering from a dangerous political malady: "boredom". Elsewhere, he said, from Spain to the US, students were protesting about wars or fundamental liberties. "French students are mostly concerned that the girls ... should be able to visit the bedrooms of the boys, which is a rather limited conception of human rights." Not so limited if you are French, aged 20 and the sexual revolution is already well under way in the United States and even in supposedly frigid Britain.

The right of young adults to have sex with one another in their rooms was, indeed, one of the first of the demands of students at Nanterre University, which led directly to the events of May 1968. Sociology students at Nanterre, led by a 22-year-old, red-haired, French-born German called Daniel Cohn-Bendit, successfully used sexual oppression as a symbol for political and spiritual oppression. .........

By 22 March 1968, the issues were much wider, including the Vietnam War. Cohn-Bendit led 300 students in an occupation of the admin block at Nanterre. Several students, including Cohn-Bendit, were accused of "agitation" and threatened with expulsion.

A demonstration in support was planned in the courtyard of the venerable Sorbonne, in the centre of Paris's Left Bank, on 3 May. A far-right-wing group, Occident, enflamed tempers – and pumped the left-wing students with self-righteous adrenaline – by threatening to attack the "manif" (demo).

The police scattered the "righties" and then began to remove the "lefties" from the Sorbonne. The demonstrators had been promised that they could leave freely. About 400 of them were brutally arrested.

Larger demonstrations gathered. The first "pavés", or cobble stones, were thrown at the police. The Paris police, supported by a few busloads of the notorious CRS riot police, responded with indiscriminate baton charges and volleys of tear gas, assaulting students, journalists, passers-by, tourists, cinema-goers and elderly couples who were sitting at café terrasses watching the fun. Many of the younger victims, and some older ones, joined in the riots. By that night, there were barricades all over the fifth arrondissement.

A week later a large crowd of students tried to "liberate" the Sorbonne, which had been ringed by the CRS. Trees were ripped up, cars overturned and cobble stones hurled – exposing yards of sand, and leading to one of the best-known anarcho-libertarian sayings of 1968: "Sous les pavés, la plage" (Under the cobble-stones, the beach).

On 13 May, the trades unions – against the better judgement of their own leaders – called a one-day strike and demonstration. The government ordered the CRS to withdraw, and an immense student and worker demonstration choked the Left Bank. But the strike did not end after one day as the union leaders planned. Eight million workers went on indefinite, wildcat strike, the largest labour stoppage in French history.

The demonstrations spread to provincial cities. A half-hearted attempt was made on 24 May to burn down the Bourse (the Paris stock exchange). The Prime Minister, Georges Pompidou, began secret – and then public – negotiations with the unions. Cohn-Bendit was expelled from France, returned and was expelled again.

Parts of the Left Bank of Paris came to resemble giant debating chambers, in which anyone who wished could discuss, endlessly, the future of humanity. At the 18th-century Odéon theatre, beside the Luxembourg gardens, there was an all day and all night, open-ended conference between, among others, Renault car workers, students, cleaning ladies, tourists, celebrated writers and artists and businessmen with nothing to do because

their factories were on strike. In the wings of the theatre, young men and women performed loveless sexual acts never previously seen on the French stage.

On 29 May, De Gaulle left France for Baden-Baden in West Germany. Crazy rumours spread that he had resigned or that there had been a military coup. In fact, De Gaulle was talking to the French military high command, making sure that they would support him.

The next day a carefully managed, but huge, counter-demonstration by De Gaulle supporters blocked the Avenue des Champs Elysées. The President called early elections (which he won easily the next month).

To the fury of the students and the more revolutionary workers, the trades unions accepted a generous, capitalism-preserving deal from the government: a 10 per cent increase in all wages and a 35 per cent increase in the minimum wage, a shorter working week and mandatory employer consultations with workers. Right wing economists argue that France's post-war prosperity ended that day, though in fact it continued until the mid-1970s and the first oil crisis.

By early June, the strikes and the student demos had melted away. France was saved. Utopia was cancelled, or at least postponed.

What remains of May 1968? Some left-wing thinkers of the time have – like William Wordsworth before them – become grumpy and conservative in their old age. The philosopher Régis Debray, a minor figure in the events of 1968, argues that, far from a left-wing revolution, "les évènements de Mai" let loose the individualism and the ultra-capitalism of the 1980s and 1990s. Under the paving stones, the beach; under May 1968, Margaret Thatcher and Ronald Reagan.

But this is once again – in the French way – to mistake May 1968 for the whole of the Western zeitgeist of the late 1960s. If anything survives of May 1968, the month and the myth, it is the tendency to romantic absolutism of the French Left. What other developed Western country could produce four (or was it five) Trotskyist candidates in a presidential election? French social democracy is still paying the price for such dogmatism, which is quite alien to the best of the free-wheeling, mind-opening spirit of '68.

This, at any rate, is the argument made by a 62-year-old Green German Euro MP who played a part in the "events of May" in Paris. "I say forget May 1968," he said. "It is finished. Society today bears no relationship with that of the 1960s. When we called ourself anti-authoritarian, we were fighting against a very different society."

The Green German Euro MP is now a pro-market, pro-European, libertarian liberal and ecologist. Like the best of the "soixante-huitards" (sixty-eighters), his mind is still open to new ideas and changing times. His name is Daniel Cohn-Bendit.