Thirty-five years ago, as men in cravats tried to discern the significance of the sexual revolution, fears abounded that, by the turn of the century, there would be little else to movies but rutting and grunting.

Sure enough, in 2004, the final taboo was broken when 9 Songs - during which actual people have actual sex - was passed for distribution in Britain and Ireland. Now Ang Lee, winner of an Oscar for that gay cowboy flick, brings us the lubricious Lust, Caution. One of the festival hits of the last 12 months was , a documentary following men who have sex with, well, just consider the title.

So, is cinematic Babylon upon us? Hardly. The three biggest films at the world's box-office in 2007 were Pirates of the Caribbean: At Worlds End, Harry Potter and the Order of the Phoenix and Spider-Man 3. You have to go down to the 17th most lucrative film, Knocked Up, to discover anything vaguely approaching raunch. Even the late Mrs Mary Whitehouse, tribune for the easily offended, would have difficulty inferring a coming moral apocalypse from those figures.

When Lust, Caution was saddled with an NC-17 certificate in the United States it was, with some justification, seen as an economic death sentence. Appallingly, many cinema chains refuse to screen NC-17 releases and, since the certificate was introduced in 1990, no film thus classified has become a box-office hit.

What are the American multiplexes frightened of? A cursory examination of box-office receipts over the past few decades demonstrates that, despite the grim prophecies of Mrs Whitehouse and her followers, only a minority of viewers relish the prospect of watching explicit sex in the cinema. Personal censorship has proved far more effective than the corporate- or government-sponsored variety.