Alison Steadman: Enter Alison the director

After years of being the muse for her ex-husband, the film-maker Mike Leigh, the actor Alison Steadman is ready to move behind the camera, she tells Maureen Paton

As if one well-known film-maker in the family weren't enough, Alison Steadman is now thinking of becoming a director. It's early days yet, as she is the first to emphasise, and this most prolific of actors certainly won't be giving up the performing career that has given her the useful and lucrative status of a national treasure. But after a successful stint last summer of directing students at her former drama school, plans are now brewing in the Steadman brain for a short film and a documentary within the next two years. That would be following in the footsteps of your ex-husband Mike Leigh, then, Alison?

Steadman looks sternly at me, a sudden chill seeping into her natural friendliness. Like other national treasures - Bill Nighy, Julie Walters - the nimble-witted Steadman manages to be naturally funny off-screen as well as on. But the subject of the reputedly moody Leigh is a no-go area, despite the fact that she attended his 60th birthday party earlier this year with their two sons, 24-year-old Toby, an illustrator and animator, and 22-year-old Leo, himself a fledgling film-maker. Steadman and Leigh each have a new partner - she lives with another Mike, the actor Michael Elwyn, whom she describes as "wonderful and brilliantly supportive" - and post-divorce relations seem civilised enough between the former couple who were once one of the most famous creative partnerships in the business. But doorstepping by tabloids followed my first interview with Steadman four years ago when she talked unguardedly about still seeing her ex-husband all the time; and the experience has left her bruised. She concedes she'll be seeking advice from film-makers about the technical side when the time comes, but won't name names. "I know how to direct actors, but directing cameras is not my field," she admits.

The wonder is that it took Leigh's former Muse so long to realise she could step out from behind his shadow, as it were. Protestations of shyness may sit oddly on someone who stripped off for her professional debut at 22 as the precocious schoolgirl Sandy in The Prime of Miss Jean Brodie and who invented the Essex Girl with the role of the brazen Chigwell chatelaine Beverley from Abigail's Party, but the unassuming Steadman describes herself as "a bit of a scaredy-cat. Many a time over the years I would phone my mother up and say I was really scared about a new role. Now that Mum is dead, my eldest sister has taken on her role. I phoned her up with my last stage show and said, 'It's a nightmare and I don't know what I'm doing and I don't know my lines.' She sounded just like my mother when she said, 'Come on, you can do it, you'll be all right'."

In her 57th year, however, Steadman has finally summoned up the courage to direct other people. "It's an age thing," she admits. "At my age, I'm looking at expanding things. I had always said I would never, ever direct because I never had the confidence in the past to even think I could do things like that; it's only now I'm in my late fifties that I've begun to think in those terms. I was asked and asked to go back to my old drama school, East 15, to direct the students and I suddenly ran out of excuses, so I did three rehearsed readings of a one-act play and put it on with basic props. As soon as I did it I wondered, 'Why didn't I do this before?' I loved it, absolutely adored it, so I'm going back there to do some more directing in January. And now that I've got a taste for it, I would like to make a short film - and I've already got an idea for a documentary."

Her range is expanding in other directions as well. As a comedy actress with a gift for the grotesque, she remains unbeatable, though she is still smarting seven years on from a put-down by a purist Janeite on the set of BBC1's Pride And Prejudice when Steadman courted controversy as a vulgarian Mrs Bennet. In the New Year special of the ITV comedy-drama series Fat Friends, however, the actress provides a long-overdue reminder that she can make audiences cry as well as laugh with a performance of subtlety and restraint as a mother reunited with the son she gave up for adoption. Next spring will see her back in the familiar territory of satirical comedy with a seven-part series for BBC1, The Worst Week of My Life, which she describes as an "upmarket Some Mothers Do 'Ave 'Em".

"I never wanted to get stuck in one groove; at drama school 30 years ago my main thing was to become as versatile as I could by impersonating people. To me, the idea that on television you get stuck playing one role is a real nightmare," says Steadman, who regards the flexibility of the Fat Friends format, in which each character has their starring turn in the spotlight, as the nearest televisual equivalent to a theatrical repertory company. A regular television gig such as Fat Friends offers security but theatre continues to be her favourite gymnasium of the imagination, and she is currently deciding whether to do a new play she's been offered in the West End in 2004 after a short tour. "I could never see myself giving up acting because my favourite place of all is on stage in a show; that's where I feel most at home, when I can listen to the audience and play them. That's my happiest time ever in life."

Yet despite her Evening Standard and Olivier awards as Best Actress and her OBE in 2000, the self-deprecating Steadman remains unconvinced of her star status. "I don't know what stardom is," she protests. "I don't know where it begins and ends. All I know is that I wanted to be an actress since the age of nine. I love the business, I love actors and being with them. I just want to do good work to the best of my ability. To actually set out to be a star is something that never crossed my mind. And everything that happens to me is a surprise; I was shocked by my awards."

The confidence, it seems, still has some way to go. Despite that debut at 22 as Sandy, Steadman shivers at the thought of ever joining the trend for newly fashionable nudity in actresses of a certain age. "I didn't mind stripping off at that age," she says with a grin, "but I wouldn't do it now - not even for Mrs Robinson."

'Fat Friends' begins a new series on ITV tomorrow at 9pm. 'The Worst Week of My Life' will be shown on BBC1 in the spring