Gertrude – The Cry, Riverside Studios, London

An orgy of courtly love

The hero's mother in Hamlet, Gertrude, is a tantalisingly opaque figure. How much does she know? What game, if any, is she playing? It's a sketchily characterised role that disappoints many of the senior actresses who gloomily graduate to it. In Howard Barker's Gertrude – the Cry, Denmark's Queen ceases to be a mystery woman – with a vengeance.

At the start, she strips naked while Claudius pours the poison into her husband's ear, and the King, in his dying agony, is treated to the porn-show of their fornication. At the funeral, her idea of wifely respect is to give her lover a vigorous blow-job before the embarrassed mourners. And afterwards (excellently played by the leggy Victoria Wicks), she swans around the court in wispily provocative see-through outfits more redolent of Penthouse than Majesty.

Howard Barker has never resented having to lend a helping hand to characters in the great works of the past. He's a dramatist selflessly prepared to roll up his sleeves and liberate these unfortunate people from the constraints of the outmoded moralities in which they are imprisoned.

Who could forget his revision of Uncle Vanya in which the personnel rebelled against what Barker sees as Chekhov's melancholy celebration of paralysis? The hero got to shoot straight, for once, and actually killed the professor. Astrov raped Helena. Sonya strangled Astrov. See what can be achieved with a bit of will-power.

Describing himself in the programme as "a tragic writer not burdened with Shakespeare's religious sentiments", Barker is here determined to rescue Gertrude from an ethos that requires shame and regret from transgressors. In this wholesale rewrite, the main protagonist is the Queen's defiant libido.

Tom Burke's very funny and touching Hamlet is a perambulating parody of schoolboy censoriousness. When told that his new half-sister smiled shortly after birth, he rejoins: "Who would not have smiled to escape the fetid dungeon of my mother's womb?" There's no paternal ghost or injunction to revenge in this version, but Hamlet is not short of problems, especially when his best friend, the Duke of Mecklenburg (Justin Avoth), seeks his help to get into Gertrude's knickers.

The actors in Barker's own staging are perfectly attuned to a style that teeters between elevated intensity and knowing absurdity. Their conviction is infectious. But there's still something stifling and hermetic about a piece that so relentlessly reduces people to their erotic drives. You'd never guess that these were folk with a country to run and a tricky succession to handle. "I have an army on the frontier – show me your arse," Mecklenburg orders Gertrude, which is as near as anyone comes to making a foreign-policy statement.

There's a lot of talk about "the cry" of female ecstasy, which seems, for Sean O'Callaghan's impressive Claudius, to be the gold standard of authenticity and an expression of shattering existential extremity: "It kills God". The difficulties with that view, and the strain it puts on Gertrude, are clearly important to the piece, but the logic of the lovers' changing perceptions is very hard to follow. And we're given so little information about the deceased king that it's impossible to decide how sympathetically to view Gertrude's refusal to feel guilt.

These obscurities are somewhat ironic, given the unrestrained, subtext-free explicitness with which the characters habitually bang on at each other. At one point it's decided that "from tomorrow the crime of understatement will carry a penalty of death" – in the world of Howard Barker, a statute of epic pointlessness.

To 2 November (020-8237 1111)