The following apology was printed in the Observer's For the record column, Sunday November 16 2003

ITV's one-off drama Reversals, to be shown on Wednesday, is written by Tim Loane, not, as we said in the article below, Tim Luscombe. Apologies.

It seems that everyone loves men dressed up as women - from Victorian pantomime and commedia dell'arte to RuPaul advertising Mac cosmetics. The funny thing is that society finds a woman dressing as a man far more troubling, unless of course it's Marlene Dietrich in black-tie drag.

Cinema is obsessed by sex-swap drama: Some Like It Hot was voted the funniest movie of all time by the American Film Institute, with Tootsie coming in second place. It's no surprise that the entertainment industry loves cross-dressing, with its multiple plot lines around disguise, deceit, seductions and mistaken identities, but what do these films say about us, the audience? Why are we so fascinated by people swapping wardrobes? Are they acting out our deepest, darkest fantasies, or do we just want our partners to experience what our lives are like for a day?

Psychologist Oliver James says: 'I think it is a matter of profound interest because as children the sense of gender is, to a large degree, socialised. So we have to learn "what a boy is" and "what a girl is". Even as grown-ups it remains a matter of intrigue to us to know what it would be like to give birth to a baby, what it would be like for a man to be a woman. So I think that Freud was absolutely right about our primordial bisexuality, our androgyny.'

James thinks that cinematic portrayals of cross-dressing resonate because 'there is a significant element of performance in being a man or a woman. For women it must be very intriguing to think what it would be like not to be stuck in a box because of how fat you are, how pretty you are or what your skin's like.'

Mainstream Hollywood presents cross-dressing as an innocent disguise (Tony Curtis and Jack Lemmon join an all-girl band in Some Like It Hot to escape the mafia; Robin Williams slaps on the drag to become a nanny to get access to his children in Mrs Doubtfire). Vital to the plot is the fiction that they have entirely bona fide credentials for 'male-femaling'. But the most interesting films dare to hint at a society where limited definitions of gender and identity do not exist. More recently we have seen the progression of gender blending from comedic device towards accepted identity - with films like Boys Don't Cry and The Crying Game where the characters' transvestism is realistic and treated with more sympathy.

Julianne Pidduck, lecturer in film theory at Lancaster University, says: 'Part of the fascination of cross-dressing has to do with role play - with seeing what happens when a certain kind of a body moves into a different role. If you think of Tipping The Velvet, Rachel Stirling playing Nan is able to walk through London relatively safely, and has a kind of erotic freedom of movement that comes with simply shifting from a dress to trousers. Within the constraints of prime-time television I thought that was groundbreaking.'

Now we have ITV's new one-off drama, Reversals, written by Tim Luscome, creator of Teachers. Billed as a screwball romantic comedy, Reversals is arguably the first time that a couple have swapped genders on screen. For Luscombe, the attraction of sex-swap comedies like Some Like It Hot is that they give male access to a privileged female space. 'There is a forbidden quality but also an innocence. But I wanted to look at the modern world. While in theory the gender roles are more equal now, in reality men and women still find it very important to define their difference. You know that classic moment when you say to your wife, "But you don't understand me!" '

Reversals is pitched defiantly at the mainstream. It stars Sarah Parish of Cutting It fame and Marc Warren (from Band of Brothers and State of Play) as gynaecologists who work in the same hospital. He is continually getting promoted while she hits the glass ceiling - so she decides to turn the tables. Arriving ahead of him at his new workplace, she takes over his name, his gender and his job title. In turn, Warren agrees to be her for a month. As Parish sees it: 'I think people love cross-dressing because they're always fascinated by what the opposite sex think of them. When someone dresses up as "you", they are basically telling you what they think of you. We're fascinated to see which traits they pick out as important or sexual or appealing.'

Reversals is broad brush comedy but there is a subtle feminist pull. Luscombe says: 'Some people will watch it and feel uncomfortable. Before I wrote it I did read up on my Anthony Clare and the crisis in masculinity, which was something I wanted to explore in a light, fun way. I chose the setting of medicine, and more particularly maternity issues, because that is an environment when the man, the consultant, is automatically in a position to be overbearing. And when you have a woman pretending to be a man looking after issues of women's health, there's huge potential for irony.'

One of the interesting things about Reversals is the way it prioritises the woman's journey. In cinematic terms, cross-dressing is less about slapstick and more a way for women to escape their prescribed destiny. Yentl, The Ballad of Little Jo, Victor/Victoria, all show women finding education, independence and travel simply by donning pants. As Luscombe sees it: 'The woman dressed as a man is less likely to be immediately funny, and we're going more to listen to what she has to say - and see what kind of story it is.'

Reversals is a brave move for both actors (several big names firmly turned it down) but Parish relished playing with her gender. 'I saw the script a long time ago when the producer was pitching another drama to me. He said: "Oh, there's something else, but I'm sure you won't be interested in doing it because you'd have to play a bloke." And immediately I went, "I'll do it!"'

An RSC movement coach was brought in to loosen up the actors. Although both Parish and Warren could 'pass' from a distance, there isn't an obsession with making them totally believable. The make-up artist decided against giving Parish facial hair and body padding, while Warren has breasts but is dressed in modern Jigsaw separates.

Parish found that playing a man had some advantages: 'I'm usually the one who has to get up an hour earlier than everyone else to have my make-up done but this time Marc was in the chair for a good hour, having his eyebrows plucked. In between takes the make-up woman always pulls and powders you - when that's the moment you want to be still and think about what you're doing. But for four weeks I could do that, which was fantastic.'

Warren's performance is fey rather than camp. At times I found him strangely attractive. Was I responding to his vulnerability? Or even to the fact that even a parody of femininity can be sexual? 'I suppose you could argue it brings out the man in you,' argues Oliver James. 'I guess more profoundly, and more likely, it's the excitement of knowing there's a secret and it's hidden - and that the man is labile and available for possibilities.'

Pidduck thinks it may be a fantasy or a yearning for a more compassionate masculinity that would have a better understanding of female experience. 'If you think about Curtis in Some Like it Hot, part of the fascination is to see such a beautiful young man and the blurring of very strong gender roles. Cross-dressing is always about a bravura performance on the part of the actor, so when we watch Greta Garbo, Julie Andrews or Katharine Hepburn, there's already an eroticised quality for the audience.'

Reversals flirts with bisexuality when Parish and Warren go on same-sex dates. Parish says: 'Whether you're cross-dressed or not, your ego still stays intact. I found myself becoming more masculine and forthright as filming went on, like the scene where I say to the nurse, "Great arse!" And Marc definitely became more feminine over those four weeks.'

There are serious flaws with Reversals though. Some of the jokes misfire and there isn't a serious gay character in sight. But it's a brave piece of commissioning in a week which saw six men suing Sky TV after 'mistakenly' kissing a transsexual on the reality dating show There's Something About Miriam.

Pidduck says it's no coincidence that cross-dressing is also cropping up on late night reality TV. 'There is a kind of slightly sordid fascination with gender-bending, drag and transgender as an exotic sub-culture or outlaw sexuality which is really quite exploitative.'

Reversals offers a prime-time drama where men can kiss men and women can wear the trousers without anyone claiming emotional damage. Producer Jake Lushington concludes: 'This is not the most radical piece in the world but I hope there will be enough playful danger and modernity in it for people to enjoy it. We're either going to get castigated for being appalling and retrogressive or hailed as the champions of the new world.'

· Reversals is on ITV on 19 November