The one thing I cannot understand about the career of Diana Rigg is why she hasn't made it really big as a movie star. She's made films, of course; after all, she was the brief Mrs. James Bond in On Her Majesty's Secret Service, and she conquered the small screen with 52 episodes of The Avengers as the liberated pistol-packing Mrs Emma Peel in black leather gear with a neat line in karate chops. She's a brilliant stage actress notching up triumphs in the great classics.
Well, perhaps Evil Under the Sun (This year's Royal Film) will prove a turning point.
Does Diana have any reason why films have not been her true forte?
"I keep trying because it's something I've so far failed at and I want to prove that I don't necessarily have to fail. I still find it difficult to divulge to a machine. The camera hasn't yet drawn out of me what people draw out of me," she explains.
Evil Under The Sun is the latest film adventure of that Belgian sleuth Hercule Poirot (again played by Peter Ustinov).
Diana's part is that of Arlena Marshall, a retired showbusiness star who, even as a chorus girl, could always throw her legs higher, and wider, than anyone else. She is one of a privileged group gathered on an idyllic island in the Adriatic during the high summer of 1938 in a luxury hotel. A murder is committed. There are nine suspects, all with motives and cast-iron alibis.
Arlena is holidaying with her most recently acquired and already long-suffering husband (Denis Quilley) and sullen step-daughter (Emily Hone).
"Arlena's a bitch, a real bitch," says Diana. "The one that everyone loves to hate. She's a disappointed woman. Not the star she thinks she should have been, certainly no Gertrude Lawrence. Well over the hill, she's not going to make it. So she marries a nice, well-off resprctable Englishman, who is never going to be enough for her with that roving eye which lights on the beauteous Nicolas Clay."
Clay plays a personable young Irishman, Patrick Redfern, on holiday with his poor little wife (Jane Birkin).
In the movie Roddy McDowall appears as a Hollywood columnist named Rex Brewster.
Said Diana, "Roddy and I tried to work out Arlena's background since he'd been writing a biography of Arlena in the film. Humble beginnings, born at the turn of the century in Tooting Bec. Sylvia Miles (who plays a Broadway producer along with James Mason) suggested her first husband was Armenian, rich-rich. We called him Zandor Zargarbian. He died and left me precisely one penny because he found me in bed with the boot boy. That's Arlena, so far..."
Diana Rigg's own background? Well, she was born in England but spent her first years in Jodpur Rajputana where her father was an official with the Indian Railways. "We went to the hills in the hot season much as the Royal Family travels to Balmoral, in our own carriage," says Diana.
Diana later attended the austere Fulneck Ladies School in Yorkshire.
"One thing happened to me at that school that changed my life," she recalls. "I was a big lumpy girl. Sylvia Greenwood (her elocution teacher) realised I loved literature, and words, and saw that I could speak and - well, act! Not just encouraged me, she cheered me on, brought me out. I began to live. I used to go home every night and lock myself in my bedroom and spout verse. So I began to think, 'This is what I want. This is being alive'. And I soon concluded that 'This' could only be made available by going on the stage."
She became, at 17, a Royal Academy of Dramatic Art student at a time when Peter O'Toole had recently graduated, when Finney was in his final year, and when the new intake included Glenda Jackson and Susannah York.
But Diana found RADA too rarified. "It had nothing to do with real life," she said. "As a matter of fact, I very nearly got thrown out because I was having a dose of real life on the outside."
She did well in her first year. "Psychologically I was still at school." But during the second year her attitudes changed. "I became fully aware of being a young woman. I made friends, went to parties. In the second year I didn't do so well. At the end of my course, I left with a plain diploma. A pass. The minimum."
She adds, "One thing I learnt was that I had a special personal problem. Others have had it too. I would have to be leading lady or nothing. Not a matter of ambition; a matter of physique. I was physically too big, too tall, to play juvenile parts, supporting roles."
At 20 she was a recruit for the Royal Shakespeare Company but in small roles for small salaries. Those were spirited days during which she gained a wealth of experience. During her five-year contract with the RSC she appeared in "Becket"; "A Midsummer Night's Dream"; "The Comedy of Errors"; "King Lear" and "Twelfth Night".
She was 26 when The Avengers took over her life. She recalls seeing one of the episodes just over two years ago in New York. "It had dated so fast," she says.
"Do you know I still get very passionate letters from small Japanese gentlemen. In America it's a sort of cult. They bring it on at 11:30 at night, along with horror movies and Carole Lombard. It's rather horrendous to be a cult in your own lifetime and to actually see yourself in black-and-white. I look like early Joan Crawford, lipstick up to there. But it was 20 years ago."
Diana has tasted both success and failure on American TV. She won an Emmy nomination with In This House of Brede for CBS, but her shirt-lived TV series Diana was a disaster.
"One writer called it 'as light and frothy as a large glass of prune juice'.
"When I arrived in Los Angeles, the studio sent this three-block-bus, smoked glass limosine to meet me. Six months later, the day I left, they sent the banged-up studio station wagon. I never stopped laughing on the plane home. 'You've failed', they were telling me, 'and just in case you didn't know it...'"
But Diana Rigg's rare failures are quickly forgotten when you recall her major triumphs such as her Hedda Gabler on our TV. The producer, Pat Sandys, described her performance as "the most incredible performance I've ever seen on television."
Her work for the National Theatre has included such varied roles as Lady Macbeth in "Macbeth"; "Phaedra Britannica"; "The Misanthrope", and Tom Stoppard's "Jumpers" a musical which tested a voice she calls "deep down transvestite".
London, Los Angeles and New York performances in "Abelard and Heloise"; a flawless Shaw, Eliza Doolittle and Stoppard's brilliant "Night and Day" prompted 'Time' magazine to dub her "Britain's Best Actress". It was during the London run of "Night and Day" that Diana was almost literally crippled by a pinched sciatic nerve, but she chose to soldier on in the face of either an operation or being six months flat on her back. She only missed 36 performances and often went on stage in excruciating pain.
"She'd rather have the pain that not act," said the play's director Peter Wood. "That's why she is who she is."
Diana's wide range of roles emphasises her extraordinary talent. "I was only thinking the other day what I'd been doing these past few years. Tom Stoppard, a film with Miss Piggy, an Ibsen for the BBC, and now Agatha Christie. You can't change gear much more than that!"
Talking again about Evil Under The Sun Diana says, "I've loved this film as an interval in one's life. One great thing about acting - it's a group effort and a group satisfaction. There's far more humility and teamwork in the profession than it's given credit for."
Diana has been busy on an anthology of criticism with the title "No Turn Unstoned".
She says she first became fascinated by reviews when John Simon in New York said that she was 'built like a brick mausoleum with insufficient flying buttresses'.
"Everyone seems to keep their really bad notices," Diana says. "Katharine Hepburn found me the one where Dorothy Parker described her as 'running the gamut of emotions from A to B'."
Sounds fun from a fun lady such as Diana Rigg who might well have had the time of her life as the 'bitch Arlena' in Evil Under The Sun which gets its right Royal send off in London on March 22.