Diana Rigg stabs at her salad. "I've never actually wanted to kill anybody," she declares. But her rich, molten voice suggests that she might have come quite close. "I've felt - we've all felt - anger, rage, humiliation, jealousy, hurt. They're part of the human condition. But when I feel jealousy, I feel guilty. How rid-ic-u-lous!"
Her deliberations on the urge to kill are prompted by her latest role as Medea, Euripides's tragic heroine who murdered her own children. Far from being a monster, Medea is a wronged woman, asserts Rigg.
"Her husband, Jason, owed her his life. I think the indifference of a husband who has left her and falls in love with another is more than she can bear. She commits the ultimate crime."
Since she first raised an eyebrow as Emma Peel opposite Patrick Macnee's Steed in the sixties cult series The Avengers, Diana Rigg has been tagged the thinking-man's fantasy, a femme fatale continually outsmarting but tantalising her male antagonist.
Rigg is dismissive of such fantasy tags. "I don't pander to that stuff; the only person I'm responsible to is myself and my profession. I was never wild in the Sixties anyway; I was too busy working."
But it is hardly surprising that she frequently perplexes her public. One night she is acting her socks off at the Royal Court for £165 a week in a schoolmarm skirt and twin-set (her recent performance in Howard Brenton's Berlin Bertie); the next she is exuding the incomparable Rigg glitz, dazzling in a Bruce Oldfield frock presenting Bafta awards.
In fact, she is a commercial star who bankrolls her work as a serious work (for Medea and Berlin Bertie) she is paid the Equity minimum of £165 a week with what she calls "piggy aid" - film and TV roles. "I'm a Yorkshire girl; practical about money."
In rehearsal, Diana Rigg is reliving experiences of past pain so extreme ("it's physical - right here") that she bangs her diaphragm.
"Actors aren't pretending. Truth is a benchmark for a good performance. We're often castigated as silly, incomplete people but actors exercise our emotions in the most healthy way possible - it's like free therapy and with wonderful words!"
Two years ago, she endured more personal and public pain when news broke of her Scottish landowner husband Archie Stirling's affair with Vanessa Redgrave's daughter Joely Richardson. The press jostled her to get her to talk and she was transparently furious - and hurt.
She is scathing about such intrusions: "I wouldn't dream of talking about something which possibly damaged a person - it's bad manners."
She is happier to discuss Medea and pulls no punches as conversation moves bracingly from crimes of passion to women's inhumanity to other women. She views Euripides's play as especially valid for today's audiences.
"Today people dampen their feelings to the extent that they're driven to therapy and analysis. But once you deny your emotions you deny yourself as a person. Medea's feelings are legitimate. Listen.." She lights a cigarette and reads: "I understand the horror.../ The rage in my heart is stronger than my reason."
But why kill her children? Diana Rigg's nostrils quiver as she replies carefully: "The Green says 'She killed to make Jason feel pain'."
In person, Diana Rigg is clever, outspoken, courageous, glamorous, bossy and uncompromising. And definitely a leader. "Unequivocal", a word she favours, aptly describes her views of a world afraid of moral commitment.
She despises the modern liberal parent: "I don't care about being popular with my daughter. I think equivocation is a great mistake." And she pours scorn on pregnant women only concerned with "buying basinettes and going to breathing classes.
"I doubt they take time to actually work out what they will pass on to their children. It's no good passing on nothing...No beliefs, no morals...?"
When her daughter Rachael was born 15 years ago Rigg became a regular churchgoer. Had church offered consolation? "Everyone talks about consolation," she growls. "Actually church is terrifically stimulating."
Rigg's relationship with her daughter blossomed in the love and security of such "benign discipline". They recently mastered a turning point: "She beat me at tennis. I swore and she was incredibly ungracious. I said, 'Look, I've been kind to you for years. Now it's your turn to be kind to me.' She understood immediately. It was like a formal handing-over."
Her relationship with the public has veered awkwardly between fawning admiration and a voyeuristic urge to see her reveal all. "It's women not men who want to read such things," she contends, "because it makes them feel better and more secure. It's a despicable aspect of our female condition."
For Rigg, women fall into two categories. First there are those who are cheered by the private misery of any female in the public eye: "These women can be savage. It's the pack instinct. Of course they've been taught it by their mothers." The others are "glorious creatures - wise, loving and uncompromising.".
"I won't compromise," she adds, unnecessarily. And neither, of course, would Euripides's Medea.
On acting Diana is at her most forthright: "I hold my profession in the highest regard. We have served society for thousands of years. It's about time it was acknowledged that we exist because society needs us."