Someone to watch over her...

Kevin Costner's claim that Diana, Princess of Wales, was planning to star opposite him in a sequel to 'The Bodyguard' has a strange kind of plausibility. The relationship between the damsel in distress and a beefy protector may have more than a touch of Mills & Boon, says Sarah Gristwood, but it is none the less a potent image, on-screen and off.

In the beginning, of course, there was Kevin Costner's original movie. Whitney Houston starred in an almost-real-life role as a singer in need of protection who wound up falling for Costner's moody minder. Just as Diana - after being rescued from kidnappers - would have done in the new movie.

In The Bodyguard genre came a couple of films, some real-life stories, even episodes of Baywatch and a wodge of women's magazine articles. Mills & Boon of course, had the ground covered already. The latest to hop on the bandwagon is the BBC, which must be thrilled by its unexpected topicality. The one-off "romantic comedy" The Student Prince (29 November, BBC1, 8.55pm) breaks with tradition in that both guard and guarded are male (Robson Green and Rupert Penry-Jones, shown with Tara Fitzgerald here), but at least everyone else on screen thinks they're gay.

The plot concerns two men, minder and mindee, attracted by the same woman (Tara FitzGerald). That's not where the real dynamics lie. Perhaps one of the more respectable appeals is that - with long-term romantic pairings no longer the common denominator - it offers, as validly as Friends or This Life, a new context in which to explore intimacy.

There are other theories, obviously. Lee Hall, author of the award-winning quartet God's Own Country and now of The Student Prince, sets it in the dramatic tradition of the clever servant that extends from Plautus to Up Pompeii, passing through Shakespeare's fools along the way. Cambridge tour guides tell the story of how one royal bodyguard got bored in his prince's final exams, picked up a pen and got a first; true or false, it's part of urban mythology, and something that has been borrowed for this story.

"It's an interesting power relationship," Hall says. "It's unclear who has the power, in what domain, and as such you can use it to explore the hierarchy. In this quite real and quite fragile form, those paradigms can be renegotiated.

"One of the things that fascinates me is the borderline between public and private life. The need to have a bodyguard - and the reciprocal relationship of being one - walks that line, with all the complications of family demands, of privacy. Plus, in general, people who need or want a bodyguard get someone from a different background to themselves. Usually there's a class imbalance - hence different views of the world, and of relationships. Put them together in an intimate way, and sparks fly.

"This story is The Odd Couple as far an I'm concerned," says the director, Simon Curtis, a veteran of the Royal Court and of Steppenwolf, and an executive producer of the BBC's Performance strand. He points out that the figure of the bodyguard has the particular appeal of the ordinary person within the circle of the famous. Our representative, in a way.

All of which, of course, may be missing the real point: the fantasy. Lawrence Kasdan's script for The Bodyguard had been 10 years on the shelf before it was shot as a comparatively small movie. It took a pounds 100m in its first six weeks of release in America alone - largely through female viewers. "It's the hairy-chested guy - the idea of a man speaking of love is much more powerful when he 'is a man'," says Robson Green, who describes the feelings involved as "primeval".

Of the feature films, Guarding Tess had its cake and ate it - the age difference meant that Shirley MacLaine and Nicolas Cage could develop their relationship in sexual safety. In Someone To Watch Over Me, Tom Berenger and Mimi Rogers played out the romantic implications to the full - although, as in The Bodyguard, it was made clear that these things were never meant to last. The almost - but not quite - unbridgeable gulf that keeps the affair in never-never land is an important part of the fantasy.

In interviews, professionals view the whole idea of a sexual involvement as both misguided and unprofessional. But it happens. Witness Roseanne Barr, Susan Ford (daughter of President Gerald), Patty Hearst and Princess Stephanie of Monaco, all of whom married their bodyguards. Why? Propinquity; Lady Chatterley stuff; a bit of rough. Or perhaps for safety. "For many women, there's an automatic emotional link between security and affection," said Dr Kevin Grold, a US psychologist who has made a study of minder- struck women.

Diana was said to be close to one of her bodyguards. So, indeed, was Princess Anne. It lends the Costner story - detailed in an interview he gave to American Premiere magazine - a smidgin of plausibility. Her office and her friends deny there were any film plans. But it seems oddly apt that The Student Prince was to have been called The People's Prince, until events forced the BBC to change the title hurriedly.