THEATRE / Avenger to revenger in 30 years: At the age of 55, Diana Rigg 'has decided to take them all on'. Profile by Robert Butler

THIS MONTH you will be able to go to the video shop, buy an old episode of The Avengers and watch Diana Rigg in her catsuit, flippantly dispatching villains without letting a hair fall out of place. Then you can fast forward nearly 30 years, go into the West End and catch Miss Rigg in Medea, a towering figure, drenched in the blood of her children, whom she has just murdered.

Diana the avenger has become Diana the revenger. Her Medea is a blistering, sardonic performance, full of sharp argument and bitter raging passion. With it, Diana Rigg - famed for her sexiness, elegance and high-kicks - challenges the leading actresses of the day with something entirely classical. More than 30 years ago Peter Brook said: 'If she doesn't waste herself on silly films she could become something good.' All Brook got wrong was the 'if'. She's done both.

There's been parenthood too, a couple of broken marriages, a flop musical and a flop American TV series: closely modelled on the Mary Tyler Moore Show, it became known as the Mary Tyler Less Show.

Today she works more for the awards than the rewards. Medea started out as a production at the Almeida Theatre in Islington, for which she was paid pounds 165 a week and received Best Actress from the Standard.

At an age (55) when others might have one foot on the brake, Diana Rigg has hers on the accelerator. 'She's done an awful lot of things,' says Jonathan Kent, director of Medea, 'but now I think she's determined, very properly, to be the great leading actress that I think she is. She's found all sorts of ways of not being that.'

Two years ago Rigg and Kent did Dryden's All for Love, last year Medea, this year Medea again, and they are planning to do The Seagull. Kent has all sorts of things he'd like to see her in: Sweet Bird of Youth, Phedre and, 'eventually', Mother Courage. 'She's an actress who's decided to take them all on,' he says. 'She's coming into her own. It's thrilling and rather moving.'

Her former colleague from The Avengers, Patrick Macnee, is modest about his own skills ('I work on the lower slopes'), but unabashed about Diana Rigg's. 'She's a poet, and she has wonderful clarity of exposition.' Speaking on the telephone from Beverly Hills, he says: 'She's one of the three great classical actresses in the world.' The other two are Glenda Jackson and Vanessa Redgrave. But what about Judi Dench? 'Ah, Dame Judi . . .' Down the line from Beverly Hills, Patrick Macnee proves himself a master of the mischievous pause.

DIANA RIGG walks into the foyer of the Bath Spa Hotel, in a designer blazer and neatly pressed jeans. She's tall, 5ft 9in, and wears heels. Her thick auburn hair frames her face. The hotel staff are dithering about arrangements. Her large brown eyes look drained of energy. She sighs, then snaps out that the important thing is to find a room now. A room is found.

In the Imperial Suite she wanders round the bedroom with its four-poster bed, bathroom and dining room, before settling at the end of a large, thick-cushioned sofa in the drawing room. She looks at home. 'Try not to read any past interviews,' she says.

It's too late. The cuttings have already shown that she once worked in a blood bank, got her mother to answer her dirty mail from The Avengers, fell out with George Lazenby while filming On Her Majesty's Secret Service, refused to sit on Anthony Clare's psychiatrist's chair, and brews her own vodka. She has played tragedy before, too - Lady Macbeth, Clytemnestra, and Cleopatra - but never with this kind of success. 'I wasn't ready before. It takes time to gather the equipment that you need - emotional, intellectual, technical - to play a part like this, which is why, traditionally, it is played by women who are too old. Like me.'

She was born in Doncaster in 1938, but left England when she was two months old. Her father, an apprentice engineer, answered an advertisement in the Times and got a job in India as a works engineer on the Rajputana railway. It's why she doesn't have a Yorkshire accent (though she refers to herself as a Yorkshire girl).

How is she like her parents? Long pause. 'I find that very hard to answer. I'd need a long time to think about that. We were a close family, we loved . . .' Then she changes tack. 'There are vast areas of me which I don't think belong anywhere.' Is that what led you into the theatre? 'I think so, yes.'

There's nothing glib about Diana Rigg. She pauses, turns questions over in her mind, decides that she can't answer one and spells out the answer to another as if chiselling an epitaph. 'My parents were rather Edwardian. I didn't see a great deal of them. Aya (her Indian nanny) was around. I saw more of my mother during the hot season when we went up into the hills.' Did you spend a lot of time on your own? 'Yes.' Reading? 'Yes.'

There are two moments she talks about where she turned towards acting. One was finding a red chiffon ballgown in her mother's wardrobe and discovering that she could be someone else. The other was sitting on her father's knee while he read to her. What stories? 'Just So, The Hobbit, the classics.' She read the same books to her daughter, Rachael, now 16.

The lonely child came back to England, to Fulneck Girls', a strict Protestant boarding school in Leeds. 'Again, I felt like a fish out of water. I knew nobody. I started from scratch. And ditto when we moved again. So I was quite a loner.' As Jonathan Kent says: 'Diana has a camouflage of candour. But she has a secret self, a private heart, which I find the most interesting thing about her allure.'

Life began at Rada - Susannah York was the year below - and the two years that followed in rep, along with other jobs, as a model and an assistant stage manager. She was an ambitious ASM: prompting the actors so much in one production that the local paper suggested she take a curtain call.

She joined the Shakespeare Memorial Theatre, later to be the RSC, in 1959, a pivotal moment. 'I was on the cusp of Glen Byam Shaw and Peter Hall's years. Glen Byam Shaw went out with a bang. That year there was Olivier, Paul Robeson, Edith Evans, Albert Finney, Charles Laughton . . . The following year there were stars, but that wasn't the main thrust. Peter Hall was building an integrated company. I was put under a three-year contract which meant I was being nurtured, I had the security and the knowledge that if I wasn't doing very much this season, then next season I might.'

Which is what happened. 'The cliche is that you go on as a spear-carrier. I was playing an Amazon lady and I did actually have to carry on a spear.' It wasn't long before she was being carried on herself, this time by Paul Scofield, as Cordelia to his King Lear in Peter Brook's famous production.

Her agent sent her up for The Avengers audition. Two days later Diana Rigg was working alongside Patrick Macnee. 'I watched his style to understand what was required of me.' Were there rules? 'Absolutely. It was rather old-fashioned. Things could be suggested, but never overt. The continuum of a series actually depends on the suspension of the relationship.' But there was a lot of intimacy. The camera moved in close as if you were about to kiss. 'It's what's in the eye. We seldom touched each other.'

The career move was looked upon with 'some disdain' by the powers that be at Stratford. But Rigg wanted to be a modern actress. Two years later she returned to Stratford to play Viola in Twelfth Night. This time her name sold tickets. 'I owe The Avengers a great deal. It's why I'm known. I've never turned my back on it.' With The Avengers, too, came the tabloids. From the Sixties on it wasn't hard to keep up with why she didn't want to get married ('nobody owns me, nobody will'), why she did want to get married ('the first time I've seriously met my match'), and why the marriage had been a disaster ('my bloody awful independence').

After an 11-month marriage to Menahem Gueffen, an Israeli painter - photographed in the tabloids with moustache, open shirt and medallion - she met up with Archie Stirling, former Guards officer, landowner and businessman - photographed in a pinstripe suit, with a raffish, clean-shaven grin - whom she later married.

The string of hits that she had in the Seventies - Heloise in Abelard and Heloise (by Mrs Thatcher's speechwriter Ronald Millar), to Celimene in The Misanthrope (in Tony Harrison's modern version) and Dottie in Tom Stoppard's Jumpers - marked out her territory: wit, vigour, sensuality. These qualities continue, to remarkable effect, in Medea. But the 'profound' change in her career came when, aged 39, she gave birth to Rachael.

She went back to work, in another Stoppard play, Night and Day, when Rachael was five months old: it produced her second famous nude scene (Abelard and Heloise being the first). 'Then I did an ill-fated musical in America and I took her with me.' Colette, a musical about the French novelist, never got further than Seattle.

'The poor little sprogget was in one nursery school then another. I realised it was impossible, that I wasn't going to subject her to this. That she had a right to have what every child has a right to have, a secure home. So that meant goodbye to any more work in America. It meant choosing very carefully what I did so that it didn't bite into the school holidays. So I could be there at the school gates to pick her up.'

She chose the bitchy actress in the Agatha Christie film Evil Under the Sun (1982), Lady Dedlock in the BBC's Bleak House (1984), Phyllis, the ice-cool socialite in Sondheim's Follies (1987), and Helena Vesey, the vengeful, jealous mother in the BBC series Mother Love (1989), for which she won a Bafta award. She was back, unhappily, in the gossip columns, when her husband went off with Vanessa Redgrave's daughter, Joely Richardson.

SHE TAKES a taxi across Bath to give a lunchtime talk at the theatre. She has two films coming up: the BBC's Genghis Cohn, to be shown at the London Film Festival, a black comedy set in 1930s Germany in which she plays a seductive baroness; and A Good Man in Africa (starring Sean Connery), in which she plays a seductive consul's wife. There's a rumour that she is going to play the lead in Pal Joey, the National Theatre's next big musical. 'I wish.'

She slips through the stage door of the Theatre Royal, behind the Medea set, and goes out to face 100 people who want to hear about her career. She sits on the edge of the stage, tugging at the neat creases in her jeans, refusing to answer some questions, managing others. What took her from Cordelia to Emma Peel? 'It was the first perverse decision,' she says, 'in a long line of perverse decisions.'

'Medea' previews Wed, opens 19 Oct at Wyndhams (071-867 1116). 'The Avengers': first six of 132 episodes out 25 Oct (Lumiere, pounds 10.99 for two episodes).

(Photographs omitted)