1968 There has never been a year like 1968, and it is unlikely there will ever be again', writes Mark Kurlansky in his illuminating book, 1968: The Year That Rocked the World. 'At a time when nations and cultures were still very different there occurred a spontaneous combustion of rebellious spirits around the world.'

1968 'There was not one '68, as popular myth would have it,' says the historian Dominic Sandbrook, author of White Heat: A History of Britain in the Swinging Sixties. 'The riots in Chicago were different to the protests in Mexico, which in turn differed from the events in Paris in May. In each case the causes were different.

What did they have in common A sympathy with radical leftist (socialist) politics A shared sense of idealism that often bordered on naivety and had its roots in the previous year's hippy Summer of Love, and a distrust of all forms of established authority including parents, police, college administrations and government. Above all they shared what Sandbrook calls 'the common spirit of youthful rebellion'. 'Youth was a new thing in the Fifties, and by the Sixties you had young people who, for the first time, were self-consciously generational,' (Sandbrook) He says. 'In America, Britain and Europe the growth of education and affluence meant that young people were suddenly defining themselves as separate from, and indeed, against the beliefs and values of their parents.'

These rebellions were not planned in advance, nor did the rebels share an ideology or goal. The one cause many had in common was opposition to America's war in Vietnam but they were driven above all by a youthful desire to rebel against all that was outmoded, rigid and authoritarian At times, they gained a momentum that took even the people by surprise. Such was the case in Paris, which is still regarded as the most mythic near-revolutionary moment of year, but also in Mexico City, Berlin and Rome.

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On March There was a big anti-Vietnam war rally in Trafalgar Square in London. Afterwards, 8,000 mainly youthful protesters marched on Grosvenor Square, where Vanessa Redgrave delivered a letter of protest to the American embassy. The crowd, refused to disperse, and a fierce battle followed between demonstrators and riot police. Protesters hurled mud, stones, firecrackers and smoke bombs; mounted police responded with charges. The violence of the struggle, in the heart of Mayfair, shocked everyone. By the end of the afternoon, more than 200 people had been arrested.

May '68 "had a big impact on the outlook of many of my generation, and on the political culture we inhabited," he feels. But then, he wonders, "What do I know? I ploughed my way through my Marcuse along with the best of them, [but] pretty soon after I was living in a commune in south London, consuming large quantities of pot and playing drums in a rock band. Then came the hallucinogens - and the world really changed."