Joan Smith: Good luck to Hugh and Jemima. Who needs marriage?

Who said "it is a truth universally acknowledged, that a single man in possession of a good fortune must be in want of a wife"? Jane Austen, although the opening line of Pride and Prejudice is, of course, an ironic commentary on the marital ambitions of the wives of provincial gentry. Next question: who is reputed to have said that a man who marries his mistress creates a vacancy? The answer is the late Sir James Goldsmith, whose daughter, Jemima Khan, has, I hope, taken better note of her father's observation than Ms Austen's.

This weekend, Khan finds herself in the unenviable position of being characterised as the second beautiful woman who has failed to get the actor Hugh Grant (pictured below) to the altar. Grant's publicist (an essential figure in the break-up of any celebrity couple) has announced that the split is amicable, and Khan's "friends" are already letting it be known that she never really felt the relationship would lead to marriage. Why would it? Grant and Khan are adults, with sufficient resources to maintain themselves in some comfort, and Khan already has two children from her marriage to Imran Khan.

They seemed happy enough together, as far as one is able to judge from glimpses of them inHello!. Speculation about a wedding has always seemed to be based on little more than Grant's clear responsibility, as a single movie star in possession of comfortable means, to get hitched at some point. The fact that his ex, Elizabeth Hurley, is currently planning extravagant wedding celebrations with her Indian boyfriend has added to the impression that Grant is that bogeyman of popular culture, the committed commitment-phobe.

This personage is much discussed among single women and students of modern manners, cited as evidence of the antagonistic relations between men and women in post-feminist Britain, the selfishness at the core of a culture of individualism or the cause of the total breakdown of civilisation (© David Cameron). This seems a heavy burden to place on one person's shoulders, especially if, as in Grant's case, the problem stems largely from the roles he plays in films. Grant has been typecast as a romantic lead, playing the charming, boyish (though he is 46), eligible bachelor who gets the girl after surmounting various concocted obstacles.

Judging by his baffled remarks about his role in the newly opened Music and Lyrics - "I'm not a very romantic man. What am I doing in this film? I don't know" - this is a testament to his skills as an actor. There was nothing romantic about his arrest with a prostitute in Los Angeles 12 years ago, although the elision between screen character and actor was powerful enough to protect his career.

Apart from the couple themselves, few people know why Grant and Khan have broken up. More interesting is the assumption that the inevitable trajectory of any relationship between a man and a woman is towards marriage. Khan's reported claim that she never expected to marry Grant will be treated as damage limitation, an attempt to conceal hurt feelings and discourage the nearly inevitable inference that she was unable to get him to pop the question.

But what if it's true? You don't have to subscribe to the old feminist slogan that a woman needs a man like a fish needs a bicycle to think that marriage is a slightly puzzling irrelevance. If Khan is a modern woman, she may have come to the conclusion that tying the knot is indeed wonderful - if you happen to be gay.