Boy Meets Girl - Strangers in strange skins

Martin Freeman had no hesitation in accepting the role of Danny in Boy Meets Girl, an engaging new gender-swap comedy drama for ITV1. He explains why. "It's something a bit different. I've never played a woman trapped in a man's body before." He pauses. "Except at home, of course!"

Rachael Stirling, who plays Veronica, the woman with whom Danny exchanges bodies, was equally eager to take on the role. "I've done five parts already about how the question of gender defines us," she declares. "In The Theatre of Blood, for instance, I wore a penis made of lentils" – as you do – "while in Tipping the Velvet, I had to pretend to be a boy. I reckon I'm the most qualified actress to play this part. In the meeting to discuss the role, I went in and said, 'you've found the right person for the job – I've already had five penises made for me!'"

In Boy Meets Girl, in the middle of a violent thunderstorm, Danny, a dishevelled, down-at-heel DIY store worker obsessed by conspiracy theories, bumps into Veronica, an immaculately soignée fashion journalist who spends more on lingerie than most people fork out on their entire wardrobe. When they are simultaneously struck by a bolt of lightning, they swap bodies.

In the first of four episodes penned by the newcomer David Allison, Veronica is left begging on the streets. In Danny's body, she frightens off passers-by by claiming she is really a woman. She is also appalled by how smelly men's public lavatories are.

Meanwhile, inhabiting Veronica's body, Danny is repelled by the idea of sex with Veronica's gorgeous, trendy boyfriend, Jay (Paterson Joseph). He also finds it impossible to put on a bra or walk in her fashionista high heels – he is constantly teetering on the brink of a fall. "I don't know how anyone can wear these," he moans to Jay. "They're like instruments of torture. Perhaps we should export them as part of our not-so-ethical foreign policy!"

The two lead actors found researching the drama a fascinating experience – they were both required to gain an understanding of the opposite sex that goes way beyond Men Are From Mars, Women Are From Venus. Stirling asserts that: "I'm not interested in all the fluffy nonsense, but I am interested in how we define ourselves as men and women. I read all of Jan Morris [the writer who had a sex change] and learned something of what happens when that sense of self-definition is taken away."

The vivacious, 31-year-old Stirling evidently put in a lot of spadework in preparing for the drama. "Every day," she recalls, "I'd have to do three hours' homework and work out who the hell I was! Martin and I studied each other like apes. Like a lot of actors, he's quite a feminine, sensitive man, and I'm quite a masculine woman, so we could steal bits off each other. I videoed Martin performing a scene as me and nicked some of his mannerisms."

For light relief, the director Alrick Riley (Spooks, The Fixer) gave the pair time to try out their roles while wandering around ITV's HQ. Stirling recollects that, "in order to learn what a man in those shoes would look like, I watched Martin tottering around in high heels – much to the confusion of the ITV office-workers!"

The 37-year-old Freeman, who recently took the very different role of Rembrandt in Peter Greenaway's biopic, Nightwatching, jokes that he didn't have to start completely from scratch when researching his part. "It's not as though I didn't have a camp bone in my body beforehand. I'm an actor, for goodness' sake! As an actor, you learn to deal with mockery, as most people think it's not a very manly job. But fortunately, as Adam Ant so aptly put it, ridicule is nothing to be scared of."

The actor, who has made his name playing such characters as Tim in The Office and Arthur Dent in The Hitchhiker's Guide to the Galaxy, remarks that, when it comes to playing the opposite sex, God is in the details. "You wouldn't notice a man sitting with legs wide open, but you'd certainly notice a woman doing that. And without mugging or copying Jessica Rabbit and doing cartoonish wiggling, you walk very differently as a woman.

"Women also tend to pick up wineglasses with their fingertips rather than in the palms of their hands. And it was pointed out to me that a woman doesn't look around as she walks down the street – it's much more contained. Blokes don't care who knows that they're looking around. Women are not so expansive – they don't necessarily want to catch people's eyes. It's the little things that make a difference."

Stirling goes on to outline what for her are the essential, psychological differences between the genders. "It's a massive generalisation, but if there is a route between A and B, boys will take the most direct, least confusing path," reckons the actress, whose mother is Dame Diana Rigg. "That's why men's relationships with men tend to be more straightforward. They're more frank, and nothing is overly questioned.

"Girls, on the hand, will follow a corkscrew route from A to B. They will keep trying to interpret what the other person is thinking. We love complicating things and supposing what's going through other people's minds. We think, 'even when my boyfriend says, "I want a ham sandwich", he probably doesn't want a ham sandwich'. We're the champions of second-guessing."

So what do the actors think that audiences will take away from Boy Meets Girl, a drama whose plot has echoes of the books Metamorphosis and Vice Versa as well as the movies, All of Me, It's a Boy Girl Thing and Big? Stirling hopes: "It will prompt the odd nightmare about what it would be like to wake up in someone else's body. After all, it's a horror that's familiar to all of us from puberty. That's a period when all sorts of out-of-control things happen to our bodies.

"This drama also emphasises the extent to which we're defined by how we look. Who we are is who other people think we are. When that's removed, we're lost. When Jay brings what he thinks is Veronica back to their flat after the accident, she starts to behave in a very male Manc way." Burping unashamedly after downing a bottle of fizzy pop, anyone? "What is normally a perfectly normal male characteristic suddenly becomes inordinately threatening when carried out by a woman. That's intriguing to watch because everything is called into question. I'm fascinated by that idea of the rug suddenly being pulled from under us."

Stirling and Freeman are a sparky double act. But there is another performing partnership audiences would be equally keen to see: Stirling and her mother. Is there any chance of us witnessing that pair collaborating on stage or screen in the near future? Stirling lets out a hearty laugh. "How many times have we been offered Hay Fever or The Importance of Being Earnest? We always say, 'God, how unimaginative.'

"The problem is, mama has more dignity than I do – I just want to be liked! I'm a waggy-tailed Jack Russell to her elegant lioness. She's Simba, and I'm Scrappy-Doo. We're not ruling out working together. But I pity the director. It would have to be someone very resilient and with the hide of a cow!"

'Boy Meets Girl' starts on ITV1 on 1 May