Theatre: Talking Heads Minerva Studio, Chichester

In the original TV version of Alan Bennett's monologue A Bed Among the Lentils, Maggie Smith's performance was merely excellent. Seen now on stage at Chichester in the author's own production, the performance is brilliant beyond belief.

This time round, of course, she's playing to an audience, not just to the camera's impassive eye. The isolation of the characters in Talking Heads and the essential unresponsiveness to the worlds they inhabit, are features that run the risk of being diluted in the theatre, where the monologists, washed by waves of delighted laughter, seem to become incongruous objects of public popularity. But though Smith plays to the audience, she doesn't play up to it. The positive feedback spurs on the actress; it does not console the character.

Wan of face, flat of hair, clutching a drab cardigan round a body that seems to have become neuter through sexual neglect, Smith brings to marvellously mordant life the figure of Susan. She's the wife of a go-ahead vicar who is too preoccupied with his career and the adoring attentions of his fan club of female parishioners to notice that he's driven his wife to the bottle and into the arms of an Indian grocer. Last to become aware of her alcoholism, the vicar is the first to take a false, career-enhancing credit for Susan's recovery, and she finds herself paraded about as the problem wife his love has redeemed.

Smith superbly captures this woman in all her phases. A mistress of nasal disdain, she's in her element delivering Susan's squiffily devastating put-downs of the smug, peevish world of the faithful ("If you think squash is a competitive activity, try flower-arranging"), the husband's embarrassing jargon ("We met it with love") and the joyless puritanism of the English to which the Indian grocer comes as such a liberating contrast. But Smith makes you aware that this character is not just a withering tongue and that she in fact asks deeper questions of life than any of the God-botherers by whom she is surrounded. In the brief, fragile wonder she communicates when describing her affair and in the heartbreaking catch in the voice when recording its conclusion, you get a piercing intimation of the more large-spirited woman she could have been. Our final view of her, spruced- up and encased in a smart outfit of clerical black and white, shows her in the ironic predicament of now having to attend two ghastly religious groups - the Church and Alcoholics Anonymous.

This masterpiece of acting and of writing is preceded by Margaret Tyzack in Soldiering On, which isn't nearly as good. A newly-bereaved widow, once "second-in-command of meals-on-wheels for the whole of Sudbury", rabbits bravely on in an effort to delay acknowledging that her son is swindling her on a vast scale and that her husband sexually abused their daughter. It's a piece that is thoughtfully ambivalent about the value of this middle-class stoicism (it may have contributed to causing what it helps her to survive). But the performance and Bennett's writing kept reminding me a bit too insistently of Joyce Grenfell's "Lumpy Lattimer".

To 29 June. Booking: 01243 781312