Redgrave with daughter Natasha Richardson, who died last year from a freak brain injury after a minor skiing accident. Image Credit: Wenn

How to address Vanessa Redgrave is the question. She's 73 and a living legend, so to call her Vanessa feels far too cheeky. But Ms Redgrave sounds too formal, and her married name Mrs Nero (she married her on-off boyfriend of 43 years, Italian actor Franco Nero three years ago) seems quite unsuitable for such an Amazonian creature.

"Ha ha ha," she chortles in her languid smoker's tones, when I ask her what she'd prefer. "We're going to be speaking to each other for an hour, so Vanessa is fine."

My instincts, I say, are that she should be Dame Vanessa, the third hypostase of the Trinity whose other members are Dame Judi and Dame Maggie. But Redgrave, in keeping with her reputation as a champagne Trotskyist and enemy of the Establishment, is rumoured to have declined a damehood in 1999. Is that true? "Even to talk about the subject would be totally incorrect, lèse majesté," she reprimands, gently but sternly. "I always say my greatest honour is being a goodwill ambassador for Unicef."

This is a typical Redgrave response: long-winded, gracious, yet grand, underlining her rejection of personal glory for the greater good of humankind. For decades she's championed every radical cause imaginable.

An impregnable stateliness surrounds her, as reigning matriarch of the sprawling Redgrave acting clan, that includes her siblings, Corin and Lynn and her niece Jemma. Her father, Michael, was a knight as well as a stage and screen heartthrob; her mother, from whom she inherited her slightly sorrowful beauty, was leading lady Rachel Kempson. And then there are her thespian daughters, Joely and Natasha Richardson. Natasha, of course, died last year from a freak brain injury after a minor skiing accident, aged 45. The tragedy gave the world another perspective on Redgrave, as no longer the earnest campaigner or the grande dame, but more personally as grieving mother.

Redgrave is talking to me from a "very cold and very beautiful" New York, where she is about to attend a gala dinner honouring Natasha for her work with amfAR, the Foundation for Aids Research, a charity very close to the family's heart since Redgrave's first husband (also actor and director), Tony Richardson, died of Aids in 1991.

"It's going to be quite a night," she says, before adding surreally, "I will say a few words, Meryl Streep is going to sing for Tash and Lady Gaga will perform."

Undimmed energy

Her mother worked until she was in her '90s and Redgrave's energy appears equally undimmed. She has "two book prefaces" to write before she returns to London and will soon start filming Coriolanus, Ralph Fiennes's directorial debut; two films made since Natasha's death, The Whistleblower and Letters to Juliet, are in post-production; and over Christmas she had an unlikely but enthralling cameo in the BBC's Day of the Triffids, in which Joely starred.

Did working help her grieving process in any way? Redgrave's voice, as ever when she talks about Natasha, is dull and she sounds suddenly very old. "Instinctively, you want to withdraw but you know you have given your word and you must stick to it. The people you are working with are very understanding and very supportive in all sorts of ways. But it's very difficult."

The most striking example of sticking to her word came in October when she reprised her role in The Year of Magical Thinking, the monologue adapted from the memoir about the sudden death of the author Joan Didion's husband, followed by the death of her 39- year-old daughter.

When Natasha died in March, Redgrave was booked for a one-off charity performance the following month at the Cathedral of St John the Divine in Manhattan. Redgrave understandably postponed. "I couldn't do it. But then I promised I'd do it in October and it went very well."

But playing a bereaved mother from her new perspective was an ordeal. "It seemed to me that I'd understood the role to the best of my ability at the time. But when I performed it after Natasha's death I realised I hadn't understood anything at all. This time it was completely different. I wouldn't do it again." She continues: "I kept my word and the performance made a lot of money."

So intense are the political and family dramas, that they've often subsumed her acting career. But she's appeared in more than 100 films (and even more plays), many of which defined their eras: Antonioni's Blow-Up, Ken Russell's The Devils and her husband Richardson's The Charge of the Light Brigade. There's been a string of Oscar nominations, for Isadora, Mary, Queen of Scots, The Bostonians and Howards End and one win, for Julia.

Recently, perhaps inevitably, she's specialised in cameos of the old woman reflecting on her youth in Atonement and Mrs Dalloway. "More than 100. Wow, that's incredible," she says sounding suitably humble, but then somewhat spoils it by adding. "I have heard that figure before."

Tragedy and laughter

She's disappointingly bland on the subject of career highlights. "It's complicated, you don't want to put up one director against another or you don't want to mention the director you didn't like. But you know the film I remember most is [Sydney] Lumet's The Sea Gull, that we made on an island near Stockholm when Natasha and Joely were very, very little.

"I remember it not because it was a good film but because of the fun we had as a family, the long summer white nights and the jokes we had. The crew had worked a lot with Bergman, who was directing, and they were surprised, they said: ‘You are so happy and with Ingmar everyone's usually so miserable.' They couldn't work out how we could be so happy even when we were making a tragedy, although the great writers like [Anton] Chekhov know that tragedy and laughter are just a few steps from each other.

"Anyway, I'm rambling, but it took me a long time as an actress to learn that. Actually Arthur Miller taught me in the '70s. We were making a drama of his play Playing for Time about Auschwitz, but the characters were laughing. It was a big insight for me to realise that that was what's called gallows humour, in this case worse than the gallows, that humans need to laugh and make jokes in order to survive."

The naivety of this statement takes me aback. How did Redgrave reach her '40s before she knew (I take it she means "understood", she must have known intellectually) about gallows humour? But it makes sense. In her '30s she came across as an almost brainwashed member of the pompous, proselytising Workers' Revolutionary Party. Public reputation aside, for decades her politics subsumed her career and her relationships.

Apart from Richardson and Nero, she had a 15-year relationship with actor Timothy Dalton — they broke up after she refused to spend a Sunday afternoon with him, preferring to stand on a picket line. Most poignant was the effect on her children. In her 1991 autobiography, one unintentionally hilarious passage segues from the birth of Natasha into a lecture about unnecessary Caesareans in capitalist societies.

Another passage describes the young Natasha begging her mother to spend more time with her and less time campaigning. "Yes, she was 11 and going through a specific moment. I wish that I hadn't spent so much time on politics now, but these are kind of useless thoughts.

"What I didn't understand was that the personal and the political go together. I felt at the time I had to sacrifice my children's present for their future. It seemed an either/or. I didn't realise that by being with one's own children I would have had a better understanding of the ones who are not my own."

Where did Redgrave's tunnel vision originate? She has always claimed it comes from reading about concentration camps as a child, but few of her contemporaries saw the need to devote their lives to ideologies. More likely, I would guess that, like the Prince of Wales, her high-mindedness comes from her status as royalty — in this case theatrical. When she was born, Sir Laurence Olivier, who was playing Hamlet at the Old Vic, told the audience at the curtain call: "Tonight a great actress was born. Laertes has a daughter."

Cinema scene

She talks about how the film business has deteriorated in terms of working conditions for union members and goes on to criticise today's "force feeding" of celebrity culture to the populace.

"I may be wrong, but back in the '60s — which was another era altogether — you met people in the shops, the individual butchers because there wasn't a supermarket, the post office, which have all been closed down now, and there was time to talk while you waited your turn and people would talk about what they'd seen on television the night before and without exception they'd say: ‘Well, most of it's rubbish, they seem to think we like rubbish.' I have remained convinced that people are always looking for higher standards and don't know a way to get them."

Belatedly and despite her bereavement, it seems Redgrave has developed some humour. "Though Tash, she was the merriest," she says bleakly. "She was always more full of laughter than anyone else."

She's more plugged in to the current cinema scene than I expected. She loved Avatar and Precious and hasn't yet seen The Hurt Locker but "must, must, must. Am I right in thinking the director [Kathryn Bigelow] is married to James Cameron? Used to be married. Ah, how interesting."

After the lost maternal years, she's devoted to her five grandchildren ("being a grandmother — that's why you were born," she chuckles).

Politically, she now channels her energies into Unicef. "There've been misunderstandings in the past, mainly by the media, but eventually if you just speak and do wisely and well, people will understand. You just have to stay firm and stay patient, to put an end to bitter and extremely stupid polemics. Stupid, because there's so much ignorance. Anyway, I'm rambling."

There's something touching about Redgrave's optimism, that after all the mockery she can still have faith in human nature. Does she regret her infamous anti-Zionist Oscar speech? "I don't," she says deliberately. "I regret where I wasn't able to clarify calmly enough but nevertheless I don't regret saying what I said as I best could."