Harold Pinter casts a rare, revealing eye on adultery and its constant companion, mendacity, in his indelibly fine account of a triangular love affair in late Seventies literary London.

The revelation of Roger Michell's passionately acted production, in which Toby Stephens and Sam West give sensational performances, is that adultery and marital breakdown no longer seems to be Pinter's central interest.

At Betrayal's 1978 premiere everyone was fascinated by the way Pinter unfolds his account of a furtive, nine-year affair in reverse chronology, beginning after its end and tracking back to its beginnings when Stephens's Jerry first kisses Emma, (Dervla Kirwan), wife of his best friend, West's Robert.

In Michell's production, with William Dudley's white muslin drapes swirling artily around the stage, Pinter's flash-backing procedures allow something more than secret sexual attachment to loom large.

In the last scene, a sexy prelude to the affair about which the audience knows plenty, Robert virtually catches his wife in the enthusiastic arms of Jerry.

West reacts to the incident with inscrutable calm and reserve, as if nothing has happened. He accepts the arm that the effortlessly deceitful Jerry places around his shoulder as if nothing had happened.

He then briskly leaves them and the room. His behaviour conveys the impression he has guessed what has happened but will say nothing.

I now recognise Robert's silence as the predominant, characteristic sound of a play in which all three characters go in for deception, concealment and secrecy.

We witness characteristic Anglo-Saxon social behaviour: refusal to face or discuss intimate, painful things; preference for neutral politesse and vacuous exchange of banalities; diplomatically turning a blind eye.

So some years into her affair Emma admits the fact to her husband, but never tells Jerry of her admission. Robert condones the relationship and never speaks to Jerry of it, at least openly. Secrecy and silence become life-style tactics by which the trio ensure that two marriages somehow keep going.

The men have even betrayed their earlier literary idealism: Robert, the publisher, hates literature. Jerry chooses writers who make money rather than serious reputations.

In this least Pinteresque and most straightforward of all his plays, one which lacks the familiar whiff of menace or the shift between dream and realism, the lovers who lie together, lie to each other. It is the Anglo-Saxon way until reticence becomes unbearable.

Despite the edgy introversion of Betrayal's characters and their irritating excess of social, very small talk, Michell's production rivets the attention. Genuine emotion, that dreaded, un-Anglo Saxon attendant at any feast of confession and plain-speaking, memorably breaks out. Dervla Kirwan Emma's, too often affected, gushing and artificial in tone, is impervious to it.

West's superbly observed Robert, in old-fashioned clothes and invested with stiff, prim formality, as if a corset had been placed round a breaking heart, finally flares up while lunching with Jerry and rages over his publishing career.

It is a terrible, displaced anger, that is really directed at his wife and the best friend for whom he may hanker erotically. And Toby Stephens's terrific Jerry, a casual charmer, shooting looks of long-lost smitten ardour at Emma after the affair is over, betray his anguish over betraying and being betrayed by Robert, with shaking voice and desperate body-language.

How thrilling to watch Pinter's characters at last shedding their inhibitions and succumbing to spiritual striptease.