When Hair was first released off-Broadway in 1967, the self-proclaimed “American Tribal Love-Rock Musical” was instantly a cult classic, revered for its Bohemian presentation of hippie counterculture and progressive attitude to race, gender and sexuality. Despite the significant legislative change that has occurred over the past half-century, the opening allusions to Trumpian rhetoric over a crackling radio declaring the Vietnam War highlight that, on the 50^th anniversary of this landmark musical, the points made are as poignant and relevant as ever.

The premise of Hair is fairly simple; a tribe of young hippies living in outer-city New York immerse themselves in a lifestyle of sex and drugs in a bid to forget about the conservative society that awaits them in the real world. The ultimate story arch, which comes slightly out of nowhere but nonetheless makes a poignant focal point for the second half, concerns Claude, one of the tribe, who must decide whether to stick to his pacifist principles and resist the draft calling him up to serve in the Vietnam War, or assuage the social pressure from his conservative parents and broader society, demanding him to fight.

The plot may not be complex, but then again, you don’t watch Hair for its storyline. You watch Hair because this joyous celebration of an infamous counterculture sings of progress, change, and ultimately hope, and it is impossible to leave the theatre without feeling inspired.

While some of the raunchier content – such as the infamous nude scene at the end of the first act – might seem slightly less shocking to us today, director Jonathan O’Boyle doesn’t shy away from making some bold decisions to emphasise the sexuality that pulsates throughout the play. From Berger giving a member of the audience a lap dance at the beginning of the first half, to the imaginative use of props, and the fact that a performance has been scheduled in which the audience, as well as the cast, are naked – these decisions, that could come off as gratuitous shock factor, really feed into the general sense we get of a primal celebration of human interaction and the human body.

It is the cast who really bring to life this joyous celebration, adding vivacity to the drug-induced mayhem in a way that makes the escapism seem welcoming, rather than inaccessible. Particularly strong is Andy Coxon, recently very good in Yank!, who struts the stage like a quasi-Jesus on acid, giving a voice to the tribe that confidently articulates the fluidity of sexuality and gender that came to be one of Hair’s most defining characteristics. While the actors seem, at times, too old to really be high-school age drop-outs, their blind optimism and naivety certainly seems convincing.

The moment when Berger tries to convince Claude to rip up his conscription papers, imploring him that they have an alternative –  “let’s just stay high forever” – is a poignant representation of the paradox they inhabit, in a world that is defined by both hope and a tragic self-deception. We, the audience, know that this microcosmic bubble is one that could burst at any minute, but the cast manage to combine this knowledge of reality with an endearing, if blind, optimism.

Ultimately though, what elevates a medium script and a strong cast to an outstanding piece of art is the intricacy of the production. Set designer Maeve Black’s ability to transform a shabby venue in the heart of Waterloo into a shrine to the summer of love, adorned with posters, hanging ribbons and surprising immersive features, has produced the finest set I have ever witnessed, wholeheartedly contributing to the communal feel of the piece, as well as celebrating the LGBTQ movement through an inventive rainbow colour scheme. As the embargo on photographs perhaps intimates, the magic of the production lies in the living experience – it truly has to be seen to be believed.

This is not to say that Hair is without its flaws – any show that was intended for a particular socio-political climate is going to have a few teething errors for an audience whose worldview is fifty years down the line. While the progressive message may have resurfaced adeptly, some of the humour feels a little dated – such as when we laugh at Jeanie over the confused paternity of her baby, in a moment that really should just be sad.

At times, as well, the message of Hair seems slightly confused. The paradoxical combination of the tribe’s hope for change, but also naïve hopelessness, is best manifested in the division between the green world of the tribe, and the real world of the audience and the adult figures in the play. This is implicitly emphasised from the off – as the audience take their seats, the tribe are already on stage, their backs symbolically turned away from us to create their own circle.

The interactions with characters from urban civilisation are also jarring; instead of offering a defiant voice of resistance, the tribe just seem slightly deluded as to their own position and propensity to continue resisting authority. Instead of viewing the tribe as rebellious leaders of a powerful movement, we are reminded that ultimately, they are just teenagers, who have simply sneaked off to the woods to smoke pot.

Overall, however, the presentation of the green world, in all its Dionysian primordiality, is an achievement that supersedes the few flaws in how the production has aged. While we might not believe in the longevity of this counterculture, we can still appreciate the voice of hope that it offers. One is reminded slightly of Mark Rylance’s defiant, but ultimately hopeless, concluding monologue at the end of Jez Butterworth’s Jerusalem.

Perhaps the final five minutes of the play are the most representative of exactly why Hair is still so powerful. The penultimate scene, in which Claude’s decision becomes apparent to the audience, is so discordantly real in contrast to the previous ethereality of the drug-induced choreography that the audience is aghast at how such a tonal shift can be achieved with merely a change of outfit.

The response from the tribe – who invite the audience on to the stage, bringing people together in song and shattering the restraints of convention – really constitutes a three-minute testament to the unbridled power of community. This optimistic final image is a representative hallmark of a play that is in equal parts hopeful, inspiring and pioneering.

Hair is playing at The Vaults, London, until Sunday 3^rd December.