Splendour in a Hare shirt; THEATRE

Skylight National Theatre, London

"My chairman keeps telling me: never look back," remarks Tom, the entrepreneur protagonist of Skylight. "In business, he says, the world was created this morning. There's no such thing as the past." David Hare's splendid new play demonstrates that in affairs of the heart, the past is not so easily discounted.

Bringing to an end three years of estrangement, Tom (Michael Gambon), rich restaurateur and Eighties man incarnate, arrives without warning at the run-down, bitterly cold North London flat of his former lover, Kyra (Lia Williams). Once on his payroll, now a born-again idealistic teacher in East Ham, she had walked out of their six-year affair when Tom's wife, who had been a second mother to her, found out about it. The wife has since died of cancer and Tom, a mass of unresolved guilt and grief, has tracked Kyra down for some overdue emotional stocktaking.

After the sweeping panorama of public life in Hare's recent trilogy about British institutions, Skylight, a three-hander played on one set, might seem like a switch to a more domestic scale. Such appearances prove deceptive, though, for the drama gradually turns into an acute study of a relationship in which private passion and political persuasion simply cannot be extricated and in which the difference between loving people in general and loving one person is explored with a particular painfulness.

What makes the play and Richard Eyre's excellent production such a taut, involving experience are the ambiguities and ironies that keep re-directing the flow of audience sympathy and stop the couple's verbal tussling from becoming a one-sided contest. Kyra has what one might call the "Hare shirt" role: she is one of this dramatist's self-sacrificing idealists. She delivers some blistering speeches against the right-wing scapegoating of teachers who are left to clean up other people's mess.

Of course, it suits Tom to dismiss her new career as essentially a conscience- salving, self-punishing flight from him. But Lia Williams's wonderful Kyra, so genuinely aglow when she recalls their times together, displays a subtly smug and unreal-seeming convert's zeal when she rhapsodises about teaching children at the bottom of the heap. She looks, at times, like someone lonely and cold who has had to huddle herself defiantly in a blanket of rectitude. With great skill, she keeps you guessing to what extent her laudable new mission is, like her preference for adulterous love, the rationalisation of an inability to commit to one person.

The play encourages the same ambivalence over Michael Gambon's superb Tom: he's a crass, sexist nouveau, but you can't deny either the scornful acuteness of his bullshit detection (bereavement counselling on the rates etc) or the piercingness of his wounded love for Kyra. While the eponymous skylight, which he built for his bed-ridden dying wife, may epitomise a belief that money can purchase everything, salvation, forgiveness and happiness included, Tom has clearly suffered the anguish of discovering this is untrue. For emotional density and depths, this is the best thing Hare has written since Racing Demon.

n In rep at the Cottesloe, London SE1 (Box-office: 0171-928 2252)

Paul Taylor