All right, Diane Paulus' production – which has transferred lock, stock and barrel to the West End from Broadway – is an evening of high-octane exuberance that does full justice to Gerome Ragni, James Rado and Galt MacDermot's near-legendary musical. Will Swenson gives a loose yet charismatic performance as hippie-in-chief Berger, and the company repeatedly spill down the Gielgud's aisles and even over the audience to make the sensation as inclusive as possible. It is entirely faithful to the mood of the original, as Daniel Kramer's 2005 revival at the Gate was not; the shrill, petulant whinge of Kramer's version has been restored to an affirmative Yippie yip. But somehow, all that seemed beside the point. I kept trying to decipher what this show, this experience means in 2010 London, and failing to find answers.
    
It is a truism that our world is no longer the one in which the show was created, but it is worth noting a few specifics of difference. The hymning of pederasty in one number can avoid censorship now only because, post-AIDS, that entire sexual vista seems fantastical. Protests against a pointless war resonate afresh, but onstage they are burning draft cards to protest against compulsory military duty, whereas in the country outside the theatre David Cameron is floating the idea of a new voluntary civilian form of National Service. Even the musical and theatrical form of the show (such as there is of the latter, with its notoriously shapeless script) are at once familiar yet incomprehensibly alien: it is now longer since Hair premièred in 1967 than it was then since the first modern musical Show Boat had opened.
    
What the show offers us now is at best a form of escapism... clambering besuited on to the stage to dance with the raggle-taggle company at the curtain call. Yet even our very notions of "escape" are now radically altered: for all that the cast kept trying to bring us into the action, the woman in front of me was unable ever to go more than 20 minutes without checking her email on her BlackBerry. Let the sunshine in? There's an app for that. Hair's 1968 London opening took place the day after the Lord Chamberlain's office ceased its theatrical licensing and censorship functions; today, though, it is we ourselves who condescendingly "license" this brief, imagined foray into counterculture. And licensed counterculture is a kind of Sunny D of the spirit.

Written for the Financial Times.