If you want to know why Voyeurz, the West End's new lesbian erotic entertainment, was doomed to critical failure you could do worse than look back at the history of Oh, Calcutta!, the Ken Tynan-inspired revue which first attempted to make sexual arousal an artistic project. Michael White, the producer of Voyeurz, will hardly need to be told any of this, given that he was also the London producer of Oh, Calcutta! when it opened here in 1970. Understandably, perhaps, his memory of the profits the show made may be sharper than his recollections of the considerable artistic reserve that surrounded it. It's also true that it fared much better in London than it did in New York, with critics generally giving Tynan's intentions the benefit of the doubt, even if they had their reservations about the execution.

But the most illuminating things said about the relation between art and arousal came from those who declined Tynan's invitation to share in the collaborative work of titillation. Peter Brook replied that the only erotic show that he would be interested in directing was a brothel, a remark I take to be a wise recognition that successful pornography has very specific ends in mind, and that anything shown in a public theatre was likely to be inherently unsatisfactory. For most of the audience, one hopes, it would prove ante-climactic, rather than anti-climactic, but the general sense of frustration would be the same. It is fairly clear, too, that Tynan was muddled in his ambitions. To one participant he wrote that he wanted "no crap about art or redeeming literary merit: this show will be expressly designed to titillate, in the most elegant and outre way". But what has elegance ever had to do with fornication? That last clause betrays Tynan's own residual conventionality, his desire to fend off the title of pornographer, which his express design ("to titillate") suggests was properly his. Michael White is guilty of similar equivocation, conceding that his ambition is to have the audience leaving the theatre eager to have sex but also using the vocabulary of "good taste" and "eroticism".

Soliciting sketches from other writers, Tynan suggested that they might either stage one of their own sexual fantasies or use a sketch to "make a comment - satirical or ironic - on eroticism". This is another retreat from purity of intention, and a telling one, because it attempts to distance the artist from the rather elementary biological response he or she would be seeking if truly intent on titillation. What exactly would an ironic erection look like, and would it perform in the same way as the ordinary kind?

The insurmountable problem here is that art asks us to be self-aware while pornography (or "erotic entertainment", if you're feeling squeamish) insists that we not be. And yet complete self-abandonment is clearly tricky in a West End theatre. One understands that in certain specialised cinemas with very low house-lights the etiquette is rather different, that the viewers each occupy a zone of virtual solitude and that it would be the height of bad manners to show any interest in what your neighbour was up to. In a theatre, though, some sense of communal experience is almost impossible to avoid -- and that is far more likely to lead to embarrassment than arousal. Indeed, the cliched phrase for embarrassment, to be "beside oneself", contains a real truth, capturing the sudden sense of self-consciousness, of being able to examine your motives and behaviour from a detached vantage point. Embarrassment is, to extend the image, a kind of out-of-body experience. Sexual arousal, on the other hand, is an in-body experience or it is nothing.

Tennessee Williams also initially refused Tynan's invitation to push back the boundaries of taste and he did so on grounds of potential embarrassment: "I suppose there is a good deal of absurdity in the kind of sexual experience I'm mostly acquainted with," he wrote. "But when you love, the absurdity is obscured." This sounds a note of homosexual self-loathing but the qualification is hardly necessary - absurdity or something worse is present in all kinds of sex. Happily love, or lust, will hide the fact in life, but in a theatre neither are truly accessible - a crowd cannot supply the necessary intimacy.

In the wake of Oh, Calcutta! Tynan planned another "erotic" project. He wanted to gather a collection of masturbatory fantasies by distinguished writers but he got a sniffy brush-off from virtually everyone he approached. The title, though, perfectly captured the essential solitude at the heart of sexual excitement - it was to be called For Myself Alone.