Tynan, Swan Theatre, Stratford-upon-Avon

He'd been the dandy king of Oxford.

He'd been the dandy king of Oxford. He'd been the greatest drama critic since George Bernard Shaw, and the voice of his generation when he praised Look Back in Anger. He was the first - and highly influential - literary manager of Laurence Olivier's new National Theatre. But then things began to unravel for Kenneth Tynan.

Behind Olivier's back, the NT board appointed Peter Hall as his successor, and it became clear that Tynan would not be welcome in the new regime. His private life split between his spouse and an affair with Nicole, a fellow spanking addict. Eventually, his emphysema exiled him to California. His debts were such that he couldn't afford not to write, but he couldn't write without smoking - an asphyxiatingly vicious circle.

It was during this last decade of his life that Tynan kept a diary, and from it, Richard Nelson and Colin Chambers have fashioned an excellent one-man show - a "Portrait of the Critic as an Ageing Man" - that is absorbingly performed by Corin Redgrave as part of the RSC's New Work Festival at Stratford.

I only saw Tynan in the flesh once, when he was part of a panel on theatre at the Oxford Union in the mid-1970s, and my recollection is that he was slightly camper and more showbiz than the mellowly musing, donnish figure that Redgrave cuts here. Also, to portray Tynan without a cigarette (held between the third and fourth finger) is like presenting Jeffrey Bernard without a drink.

None the less, Redgrave, simply sitting in a chair and with no switches of lighting as punctuation, gives a spellbinding performance. Its understated quality beautifully reinforces the hilarious steadiness of focus with which Tynan's diaries recount the assorted disasters of this era - whether he is reminiscing about a penis injury that causes the organ to "topple sideways like an axed tree", or the incendiary effects on the colon of an Indian dinner followed by a large glass of vodka injected into his anus (by Nicole) via an enema tube.

There are some preposterous attitudes on display - for example, "A humanist is someone who remembers the faces of the people he spanks" - but in general, Tynan scrutinises his melancholy and sense of failure with such clarity of insight - "Once I had not only talent, but what the English call 'character'. By which they mean the power to refrain. Now I have neither" - that the listener is not left feeling hopeless.

Thoughts of suicide recur like a leitmotif throughout the piece - "Were I to commit suicide, I would merely be killing someone who had already - to many intents and purposes - ceased to exist." But who could resist a man who, on hearing that Joan Littlewood was contemplating taking an overdose, responded: "I must write to her and insist that she goes on suffering like the rest of us."

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