Waste, Almeida Theatre, London

We've known for some time that Sam West, an admirable actor, can also direct. That much was stirringly evident during his stint at the helm of the Sheffield Crucible. But in this past year, he has begun to establish himself as a director of the front rank. First there was the Oedipal heartache he found amid the all-male hilarity of Patrick Marber's superb poker school play, Dealer's Choice. Now there's the excellent balance he achieves between the public wheeler-dealing and the private desolation in this consummate revival of Harley Granville Barker's play Waste, a piece that fell foul of the censor when it was originally shown as part of Barker's revolutionary season of new drama at the Royal Court in 1907. Give or take the odd passage that has been reinstated from that earliest incarnation, West uses the revised 1926 version in his immaculate production at the Almeida.

Waste is a remarkably astute and revealing political drama. It takes us into the cigar-wielding conclaves where fateful decisions are made and into the fierce but only partially functioning heart of an idealist of genius who is almost bound, given the nature of English public life, to wind up a failure. It shows us the intricate interaction between the two. Brilliantly played by Will Keen, Henry Trebell is a maverick independent MP who wants to disestablish the Church of England and to use the money from the privatisation for a root-and-branch improvement of the educational system. A willingness to help him steer this Bill through Parliament is his condition for joining the Tories who are on the verge of regaining power from Labour. But then scandal threatens to scupper the plan when Amy, a married Catholic woman, dies while (against his wishes) aborting their child.

Trebell has a sister, whose tartly adoring bond with him in a loneliness that's been shared from the nursery on is superlatively conveyed by Phoebe Nicholls. She says of her sibling that his affections are two generations ahead of him, a good joke that precisely captures the way in which this visionary's passion is for the future, leaving him apparently deficient in feeling for his contemporaries, particularly women. One of the main ironies of the play is that he starts to get into synch emotionally when it's too late. He clearly wants the baby that Amy, whose violent mood-swings are unnervingly registered by Nancy Carroll, is desperate to be rid of. The main weakness of the play is that it involves demonising Amy. For example, it's a further irony that the cuckolded Irish widower (finely played by Patrick Drury) renounces the power of revenge not in order to save the career of a potentially great politician but because he feels that he and Trebell are brothers in victimhood.

Portraying the central character, Will Keen is magnificent. There's a severe precision even in his dry banter. When his finger tips stroke his thighs with sexual tension, they do so in exact parallel lines. He warms only to his theme of disestablishment and then he reminds you that deserts, though arid, are hot. With splendid cameos from the likes of Peter Eyre, Hugh Ross and Richard Cordery, the scenes of political calculation in drawing rooms and smoking rooms are a potent mix here of the ancestrally shrewd and the abjectly petty. "Practical politics is party politics" is the mantra, and the loner who tries to defy the British Lion is in for a mauling. Idealists are exploited to serve the interests of privilege and then discarded.

And yet this beautifully designed production leaves you feeling ambivalent. Granville Barker was himself a Lost Leader of the English theatre and you can't help but feel that some stringent self-analysis went into the portrait of Trebell. There's a heartbreakingly methodical clear-sightedness about the way Keen's hero faces up to the fact that for his kind of man, existence is irrelevant, once crucial plans have been torpedoed. "Life for its own sake is an overrated thing," he declares, demonstrating that narrow intensity of outlook that could have made him political dynamite, if not a rounded human being. Strongly recommended.

To 15 November (020-7359 4404)