A new age of Aquarius

'It was still powerful, still good, but it didn't have the joy." So says Paul Nicholas, one of the original London cast members of Hair, of the last London revival in the tiny Gate Theatre in Notting Hill five years ago.

And that was the first London revival since 1993, when Michael Bogdanov's Old Vic version, with an unknown John Barrowman as the hippie conscript Claude, placed ushers handing out flowers in the stalls and the cast, who wore more blue denim than kaftans, waving condoms on stage during the mass sleep-in.

So it's clear the new celebratory production opening at the Gielgud Theatre – which comes direct from last season's New York revival in Central Park and Broadway – is asking us to tune in and turn on to a period piece where the Vietnam war is still running, Aids is unheard of, "masturbation can be fun" and black girls sing that "white boys are delicious".

The "joy" thing is what I remember most about Hair, not the very brief semi-lit full frontal nude scene at the end of the first act. ("Could you see if any of them were Jewish?" asked Jack Benny.) It opened in London exactly one day after the Lord Chamberlain was banned from censoring the stage (27 September 1968) and a few weeks later, when Broadway's first (and last) "tribal love rock musical" rolled down Shaftesbury Avenue, I got up on the stage at the end and danced, fully clothed, with Mr Nicholas as well as Annabel Leventon, Marsha Hunt and Peter Straker.

Well, Princess Anne and John Lennon had already clambered up there and jigged about, so I didn't see why I shouldn't. We were all a little bit hippie in the late 1960s: it always amused and delighted me that the lovely Russian lady who ran the Financial Times's New York office when I worked on the paper in the 1980s had taken over on Broadway as the character who sings the exquisite "Frank Mills" ballad.

The original Broadway cast album had been on my gramophone turntable in college for two terms, and I loved the songs and the music even more than I loved Pink Floyd and the Beatles. This music, written by a quiet, straight, Canadian church organist turned jazzer called Galt MacDermot, was something completely new and liberating in the theatre.

Except that, as critic Mark Steyn pointed out, the Age of Aquarius that was dawning was over by lunchtime and was only really heralding the Age of Andrew Lloyd Webber, who took up the challenge of fusing musical theatre with the Top 20 a little more efficiently. Hair was a glorious mess.

Still, nothing even in Lloyd Webber surpasses the 20-minute "war" sequence of the second act, or the rhythmically shifting setting of Hamlet's "What a piece of work is (a) man", or the "Let the Sunshine In" finale which moves you to tears whoever you are, and of whatever age, Aquarian or antiquarian.

As Steyn also pointed out, this was the first Broadway show with a hymn to anal intercourse and, even more radically, a song simply named after a British provincial city, "Manchester, England". And if you have trouble equating free love with stopping a war – there is no question the New York production gave a powerful and effective platform to the Vietnam protest – you just have to re-enter the cultural bubble.

At the Gate, however, Paul Taylor in this newspaper had no problem in suggesting that Hair's time might truly have come again, with the resurgence of American imperialism, the waging of another unpopular war and the replacement of LBJ with Dubya as a figure of ridicule. There was a sinister air of coerciveness in the opening call to love; sympathy and understanding at the Gate and the nudity came back in a detention centre context in Abu Ghraib.

MacDermot, who is now 81 and still composing had been called into "musicalise" the book and lyrics of a pair of drop-out chums, Gerome Ragni (now dead) and James Rado (in his seventies). Rado played Claude, the out-of-town patriot, and Ragni the leader of the Greenwich Village commune; the only significant contemporary Broadway rock musical since then, Jonathan Larson's Rent (1996), a rocked-up La Bohème, is also populated by artistic denizens of the Village.

Quite apart from its own intrinsic merits, Hair is also historically significant for launching (and, with the later A Chorus Line in effect subsidising) the important Public Theater in New York, home of many of the best American and British playwrights – John Guare, Sam Shepard, Michael Weller (who scripted the not-bad 1979 film of Hair for Milos Forman) Caryl Churchill, David Hare – under the mercurial leadership of the director Joseph Papp (who died in 1991).

Papp was going to open the new venue with a John Arden play, Armstrong's Last Goodnight, but suddenly decided to push through the chaotic show Rado and Ragni were writing on the backs of envelopes. It opened at the Public on 29 October 1967, played for a month, moved into a Broadway club called the Cheetah and then on to Broadway, at the Biltmore (where it stayed for five years while seven other roadshow versions toured the US); The New York Times raved, the Village Voice – the parish paper of the cultural underground – sneered at the commercialism and crass opportunism of the enterprise, hardly surprisingly.

The Biltmore transfer was supervised by Tom O'Horgan, a brilliant off-Broadway director who was accused of going both upmarket and downmarket at the same time, nice work if you can get it, and that's the version we had here. MacDermot's score was wonderfully energised in its anthems, its great surges of melodic declamations and pulsating acid trips, and I always remember a hypnotic sense of continuous nightmare, or was that the dope we scored (but didn't inhale) in the interval, man?

At the Old Vic, one critic took exception to all the hippie-dippiness, memorably evoking the political punch of Miss Saigon by saying that Hair, in comparison, was like playing footsie in a wine bar. And another dissenter said she spent so much time watching nudity in theatres these days she was immune to mooning.

But one great underground member (sic), Jim Haynes, the American founding editor of International Times and fringe theatre pioneer, stayed true to the cause. In a programme note he charmingly asked: "Can we not still and again become mirrors of each other's inner light and illuminate the streets of London anew with love and music?" As the streets of London were suddenly awash with cardboard box dwellings, scroungers and muggers, the question may well have fallen on deaf ears.

There is still a point to Hair, though if only to elucidate a period in our semi-shared transatlantic social history, and to marvel in a score that has never been bettered.

So Hair today may well be gone tomorrow, but its "joy" still makes the heart sing. It led not only to Rent and another great rock musical based on a German Expressionist play, Spring Awakening, this year's Olivier award-winner, but also to every new musical that struggles to sound like a rock concert and incorporate the unquenchable spirit of youth rather than something from Stephen Sondheim's bottom drawer.

Hair opens at the Gielgud Theatre, London, on 14 April