Corin Redgrave looks tired. When I meet him at his home in Balham, south London, under portraits of his youthful self and other pictures of the Redgrave theatrical dynasty, he explains that it's no pushover playing King Lear in a four-hour production six nights a week, plus twice a day when there's a matinee. He's now following that with a 90-minute monologue about Kenneth Tynan, the legendary Observer theatre critic of the 1950s.
"He was the best," says Redgrave gravely. "He had no peer. You'd have to go back to Shaw, and before that to Hazlitt. It's really hard to evoke a performance, but Tynan always knew what to describe." He quotes Tynan's "miraculous" description of Katharine Hepburn in Shaw's The Millionairess: "She glittered like a bracelet thrown up at the sun; she was metallic, yet reminded us that metals shine and can also melt." He was writing for posterity, "evoking the feeling of what it was like to be in a certain playhouse on a certain distant night".
Redgrave, son of the actor Michael Redgrave, remembers meeting Tynan. "I have a strong memory of him arriving in bright red trousers at my parents' house in Chiswick when I was about ten or 11. It was 1949, he'd just left Oxford, was preparing to launch himself on the world and was seeking introductions from leading directors and actors. He didn't realise that my father was too shy to be of any help."
When Corin was 16, he wrote Tynan a letter protesting at his demolition of a play by Derek Monsey, a fellow critic. Tynan's reply was: "You haven't persuaded me I was wrong, but I thank you for writing so passionately." Redgrave also remembers Tynan's negative reviews of his father's work: "He attacked one of the most brilliant and brave things my father ever did, playing Hamlet at the age of 50. After saying that the most important attribute of an actor is their eyes, Tynan wrote: 'Michael Redgrave's problem is that he seems to be a Cyclops. He only has one eye.' What an odd remark."
Redgrave, who dresses in elegant if understated grey, takes a hard wooden chair while I risk my back by perching on one of his treacherously saggy sofas. As his cat, a furry bundle with a theatrical purr, rubs against my shins, I ask if he has ever learned anything from reading reviews. There is a very long pause. "No, I haven't learned from critics," he says. "I'm not sure if I or any other actor would have learned anything from reading Tynan."
But Redgrave is not indifferent to critics. He likes to know when there is one in the audience. "I love to think of the audience not just as a face- less mass, but as individuals who will be affected by my performance. The presence of one person can alter an audience when they radiate approval or amusement or interest. I have felt an audience response warm in temperature as a result of Simon Callow's very infectious laugh." He guffaws in imitation.
Tynan, adapted by Richard Nelson and Colin Chambers, is based on his diaries and focuses on his twilight years, when he struggled to make a living after leaving the National Theatre, where he was literary manager from 1963 to 1969. And although Tynan's reviews remain stubbornly out of print, this is not the first play about the critic. That honour belongs to Janet Munsil's Smoking With Lulu, aka Emphysema: a love story. Talking of emphysema, Redgrave tells me that he won't be smoking on stage because he's given up after puffing away for more than 30 years.
He is wary of journalists, and chooses his words with care, not minding the occasional long pause that makes me feel as if he's forgotten his lines. "As an actor, it's an adventure for me to play a critic," he says. "I'm grateful for the chance." One of the things he admires about Tynan was his "ability to observe his own deteriorating health in a way that is utterly devoid of self-pity. I find that absolutely admirable. Actually, my father had the same quality. He had Parkinson's, but even when he was in a nursing home, attached to a catheter, robbed of his dignity, he could make others feel at ease. To free them from pity. He was able not only to prepare himself for death, but to prepare other people."
You can tell Redgrave has been thinking a lot about death. It must be the result of playing Lear and Tynan in one season. He is also struck by the self-deprecatory nature of Tynan's last diary entries. "Tynan descends into the void and dies with a smile and a joke. Terribly moving." Whether it was being among the first to say the F-word on the BBC, in 1965, or staging the erotic review Oh! Calcutta! in 1968, Tynan em- bodied the zeitgeist of the 1960s in all its liberatory wildness and exploratory curiosity. "In those days," muses Redgrave, "it was no sin to be experimental in art. I think we miss that unchained spirit now."
And what if his performance gets panned? "Oh, a bad review can bring out the best in you - it can make you more determined to show the audience just how good you are."
Tynan is at the Arts Theatre, London WC2 (020 7836 3334) until 26 March