And she's off...

These days getting an interview with the greatest actress in the world is astonishingly easy. Vanessa Redgrave presents you with a tiny hoop while she checks your treatment of previous subjects, but she has dispensed with the contract which forbade certain topics (personal life and political views) and insisted on approval, before publication, of your article. That done, you simply show up at some flyblown rehearsal room and she's all yours for her lunch break. All yours, that is, if your intention is merely to take strenuous dictation.

To begin with, she is the essence of courtesy. Her smile seems a little shaky around the lower lip, as it has often looked from the stalls, but she is gracious as she introduces me to the cast and rushes to get me a chair, when one of nine men present should really have beaten her to it. The rehearsal proceeds for The Liberation of Skopje, a script of which is not available because daily changes quickly render any existing version defunct. The director, Ljubisa Ristic, and the male lead, Rade Servedzija (both stars from the former Yugoslavia), are absent. It's icy cold and the cast are stamping rather lamely to a moody Slav song.Redgrave is struggling gamely to decipher dimly photocopied words in a language she cannot anyway understand. They all seem a mite dispirited. Redgrave takes the lead and schedules the next singalong and the session freezes for lunch.

Having charmingly cadged three cigarettes from one of the cast, she leads me off to a quiet corner and slowly makes us a cup of tea, supplying a wonderful opportunity to stare at VanessaRedgrave playing Vanessa Redgrave. Her shoulders are disproportionately wide and rangy despite her gawky 5ft 11in, and she's thinner, more fragile than her stage appearance ever suggests. Her clothes - a black-out of jeans, loose chenille top, trainers - say nothing. There's a smear of brown eye shadow on the lids of her luminous aquamarine eyes, but no trace of vanity. Her hair - a burnished copper rinse, well-cut in a boyish crop - is clearly expected to take care of itself. Her beauty is breathtaking; her presence awesome, magnificent and utterly intimidating. I could sit and gaze all day. There's a fat gold band set with a dark red cabochon on her wedding finger, but my curiosity about it feels trivial - you won't catch me asking about that. You can see at once how she could cast a spell on a stone. What is more difficult to comprehend is how the Workers' Revolutionary Party's Gerry Healy could ever have exercised the slightest intellectual fascination for her.

Following a lengthy struggle with the contents of her handbag, a lighter is retrieved and she is at last poised to talk. The purpose of her company, Moving Theatre, which is taking over Riverside Studios for two months, seems a safe place to start.

She set it up with her brother Corin, the Berliner Ensemble's distinguished Ekkehard Schall, and the director Haris Pasovic. He is currently in Sarajevo and scheduled in June to direct Antony and Cleopatra, with Redgrave in Shakespeare's best female role for the third time .

"It's always difficult to simplify," she begins. Her voice is deep and smoked, her tone cold, weary and patronising. Nevertheless, the difficulty doesn't deter her: "The question for us was what we could do as artists in this year, the 50th anniversary of the defeat of fascism. The role of culture has been fundamental, as has the role of doctors, paediatricians, in keeping up the multicultural life and the resistance of the people of Sarajevo..."

She'll hate the comparison, but she's got Mrs Thatcher's artful dodge of dismissing your question and posing her own in order to tell you only what she wants to tell you, not pausing for breath until she has delivered every last word. Any interruptions are handbagged by the unflinching progress of her opinion. And it goes on and on and on and on. Unassailably.

Eventually - third attempt - you remind her that she once said that if she ever played Cleopatra again she would direct it herself. Her response is a lengthy preamble on world geography and warfare in Shakespearian times. Then she says, "I was originally going to direct it but seeing someone else's work gives you a new view on the work you've already decided to do." She continues: "I'll be co-directing it with Haris. We've agreed on an international casting which will represent a world full of many people, many cultures, many rulers making alliances, breaking alliances..." And then, confusingly, she goes on: "I'm directing it, since things look very bad in Sarajevo, and the airport has only just reopened. But we're hoping Haris will come back." Is her vagueness genuine? Is the project half-baked? When you tentatively say that you are still unclear, she slaps you down with, "We can't spend all our time talking about that. There are other plays in the season, you know." What does it matter anyway? If Vanessa Redgrave was being directed by a traffic warden, people would queue all night to see her.

Defeated, you ask her about her recent off-Broadway performance as a flouncing Vita Sackville-West to Eileen Atkins's restrained Virginia Woolf. "Over there, they love Virginia Woolf, here they don't," she replies, and before you can ask who "they" are, she has steamed off on her own train of thought: how the play ends with the imminent invasion of Hitler's Third Reich, how Virginia expected her husband, a socialist and a Jew, to be taken off to a concentration camp, and how everyone had a means of suicide, morphine or their petrol ration, which isn't something the Americans had been through... Intriguing stuff if you had all week, though not helped by the bland delivery.

At least it reveals how meticulously she researches her roles. When she played Mrs Alving in Ghosts, she insisted on wearing a period corset. She also returned to Ibsen's original to discover when she would be addressed as "Mrs Alving", when as "Madam". From such minuscule details she builds her performances; and it's her precision and subtlety that makes them great. When Redgrave was 24, Ken Tynan wrote of her performance in The Lady from the Sea: "If there is better acting than this in London, I should like to hear of it." Since then, we have all heard of it, pretty much every time Redgrave, now 57 (the only question she answers straight), has set foot on a stage. She's a box-office dream. The director David Thacker says she is the ultimate actress in terms of reinventing the words of a play as she says them, has an abundantly rich imagination and is a total joy to work with. Our Paul Taylor says: "There is no more truthful post-Ashcroft actress than her." Critics can savage a play and then rave unreservedly about her ability to illuminate a role.

What is most striking about her is that she can be doctrinaire about almost everything, yet capable of losing herself in a character she would surely have little respect for. "That's the business of being an actress," she says and laughs, a mocking sound which is anything but amused. "It would be a terrible world if actors only played the parts they agreed with. Our purpose is to seek and understand what life is, what is happening, what it could be, along with the writers and all countries..." Here she goes, her sails billowing with her latest cause: the responsibility of the artist, the historic role of theatre in civilisation, the transforming power of art, the horror, the horror of the cuts that are preventing children from going to school matinees... Her visit to Sarajevo in 1993 was the trigger for all this, and she's been at it ever since.

You can find her earnestness dreary and her thinking mud-dled, but her sincerity and commitment are both humbling and heroic ("I am NOT heroic," she snorts scornfully). You just wish she'd be human, rather than humane, for a second. Just lighten up and chat about being a grandmother. She resists the opportunity and looks so sad that I ask her if acting makes her happy. "Well it's not as simple as that," she says and repeats it three times, excruciatingly slowly, with a glazed stare. "It's not really like that at all." She's smoked all three cigarettes now and is scrunching a tissue with one hand and running a pencil around the piping of her seat. She seems on the verge of tears. "When you've seen things that I've seen, things that are happening to children in hospitals and schools here and in Sarajevo and in many other cities, you feel, like Schindler, if only you could save more. The question I must pose is, what can I do? I feel I get much more out of acting than I put in, but it's not a choice for me, it's a process. In the ghettos they formed reading circles and read Victor Hugo's Les Misrables; to know that, throws light on the value of preserving for a few hours, or for a lifetime, the poetry and drama of the present and the past. All this is contained in our season.

"I'm afraid I must go now."

By the time she has jumped up, the clouds that had gathered have miraculously vanished, and she is once again all sweetness and light. Something else too. Triumph flashed in those fabulous eyes.

n Moving Theatre is at the Riverside Studios, London W6, 11 Apr-17 Jun (Box- office: 0181-741 2251)