Opening the ex-files

Gillian Anderson and Roger Allam are slouched together on a bed in Anderson's dimly lit dressing room at the Comedy Theatre. It's a suitably cosy setting for this curious marriage of talents: one a famous TV and film star, the other an excellent but unfamous stage actor. Both open tonight in Michael Weller's two-hander about a man and a woman on the verge of rekindling an affair. 'It's just as well we get on,' says Allam. 'It's a rather intimate play.'

Allam's role in What The Night Is For has been somewhat overlooked in the flood of interviews the play has prompted, all of them eager to harness some of Anderson's undoubtedly starrier appeal. But Allam - who was nominated for two Olivier awards in 2000 for Money and Summerfolk and yet could sit by you on the bus without you noticing him - seems grateful to be standing, at this stage of the game at least, in his co-star's shadow. 'Do I mind that Gillian is getting all the attention? Are you kidding?'

Anderson, for her part, is sanguine - after all, being pestered by press and public is something the former X-Files star has dealt with for years. Not that she isn't keen to put as much distance between that show and this one: eager to talk at length about What The Night Is For, considerably less eager to discuss anything else. 'I'm extremely boring. I live a very quiet life. Yet people keep asking me about my childhood and expect me to wander around with entourages. I rarely recognise myself when I read about myself in the papers.'

That the play taps into a very modern phenomenon, then, happily makes it particularly interesting to discuss. The plot is straight out of friendsreunited.com: two college sweethearts, both married to other people, back in touch after 11 years thanks to a casual e-mail, and now teetering on the edge of possibility. It's a play about chance and choice, about the opportunity to change your life forever and, most of all, about finding the courage to do so.

Both Allam and Anderson agree that the play will touch a nerve in nearly everyone who sees it - after all, who hasn't dreamed of getting back in touch with their first love? But it's an issue also mired in problems of a very modern kind. 'In the past, couples were much keener to work through their difficulties, go into couple counselling or whatever,' says Anderson. 'These days, people are quick to say 'this is unacceptable' when confronted by a problem in their relationship, and are quick to assume there is something more acceptable around the corner.' For Allam, the play reflects the extent to which 21st-century relationships carry the burden of unrealistic expectation. 'Blokes expect to shack up with a woman who is not only supposed to be a wonderful wife, mother and housekeeper, but a whore in bed while also being your best friend. We all expect absolutely everything these days, and it's very difficult.'

For both, the challenge of appearing in a play that is directly emotional and immediately relevant is clearly a strong one. After all, Anderson spent almost a decade applying scientific theory to the existence of aliens while Allam's CV is littered with what he calls obvious character roles. 'Last year, I was a drag queen, the year before I played Hitler,' he says. 'In this play, there's no beard or period costume to hide behind.'

There's a chance that, thanks to the attention it has attracted through Anderson, the play may prove something of a career breakthrough for Allam. For years he has been dubbed what in the profession is known as 'an actor's actor', meaning, basically, that he doesn't work much on TV. 'Of course I would like to be more famous. It offers more career possibilities. But then it can prove restrictive. Plus you get hassled when you go shopping.' As for Anderson, she, ironically, is simply happy to be on stage. 'I'm doing something I love and I'm more creatively fulfilled than I've been in a long time' she says. 'If I die tomorrow, I'll die happy.'

Booking until Feb 23, Comedy Theatre, Panton Street SW1, Tue to Sat

7.30pm, Wed and Sat mats 3pm, Sun mats 4pm, £10 to £37.50 (tonight limited availability). Tel: 020 7369 1731. Tube: Piccadilly Circus