Theatre: Swearing? I'll give you swearing

East Vaudeville, London 50 Revolutions Whitehall, London You Be Ted & I'll Be Sylvia Hampstead, London

Twenty-five years is a long time for a play like Steven Berkoff's East. Informed by the violence and sex of the East End he knew as a youth, and immersed in the prejudices of the England of its day, it should now be either a noisy period piece or a terrifying trip down bad-memory lane. Inevitably, it is a bit of both. But in style and form, it's still one hell of a contemporary play.

Its language is rich and brutal - Shakespearean lyricism, riddled with classical allusions, then pock-marked with Cockney curses - and its structure is stylised and raw. In Berkoff's physical production, the series of slice-of-life scenes are vicious vignettes. The excellent cast attack the mix of monologues and mime with a poise that's almost - unexpectedly - delicate. By the second half, the audience are so seduced by the rhythm and rhyme that applause turns each scene into something akin to a harmless music-hall turn.

Out of Mike and Les, Berkoff's strutting, sparring partners, Christopher Middleton shades it on points: his performance as Mike is unselfconsciously expressive. Tanya Franks suggests there's something more going on beneath Sylv's sexy surface, and the understated, aproned Edward Bryant is far from a drag as Mum. It's to his credit, I guess, that Jonathan Linsley, a mountain in overalls, is believable as the racist, table-thumping Dad. But, amid a torrent of vituperation, his is the one scene that seems, now, unnecessarily provocative. Its counterproductive polemic affirms that evolution may have - just - outpaced Berkoff's otherwise vital play.

Murray Gold might care to take a stroll across town to see how Berkoff pulled it off. The opening section of 50 Revolutions, Gold's brave new play, bursts with ideas about late-Nineties urban life and, most promisingly, how its dislocation is best portrayed on stage. It's structured as a fluid series of nocturnal encounters between people whose paths cross on the streets of London. Among the wanderers, there's a lovelorn actor and his non-commital lover; a new arrival and his showbiz agent; a melodramatic actress and her producer fiance; a bouncer, a nurse and two homeless girls. Whether Gold is satirising or sympathising, each of his ciphers has a voice that, at some level, rings true, while Dominic Dromgoole's direction gives the metropolis a steady pulse.

But as its plot becomes contrived, the jump-cut novelty disappears. The characters jolt rather than bump into each other, and longer, more tedious set-pieces fail to make them reflective beings. The cast cannot be faulted, except perhaps for Amanda Root's abrasive agent. Nathaniel Parker is assured as the needy actor; Claire Rushbrook is convincing as a fatigued nurse; and Nikki Amuka-Bird, as an odd- jobbing actress, is a composed blend of wide-eyed idealism and streetwise nous. But Gold's patchy writing betrays the experiences that he really understands. Three of his main characters are actors, and his self-referentiality gets the better of his social engagement, particularly when Francis Lee steals the show as the tormented writer of the play-within-the-play, "Cod With Everything".

As subjects of comedy, conceptual art and care for the elderly aren't obvious bedfellows. In Simon Smith's You Be Ted & I'll Be Sylvia, Wendy Plummer, a feminist artist, returns to her East Midlands birthplace from London. She has a commission for a piece of public art to honour the women of the town; her cancer-stricken mother is seeing out her last days in one of its old people's home. Smith makes much of the culture clash between old and new, provincial and urbane. And, when Wendy (Nichola McAuliffe) arrives, all sneers and cigarillos, we know there's going to be trouble.

Unfortunately, Smith isn't good at trouble - the play accelerates into overblown, farcical melodrama. But he does know how to send up conceptual art and the conflict between ideology and creativity. Wendy is best known for her "Abortion Pieces" - painted with her dad's ashes and her own menstrual blood. Sylvia Plath's legacy is raised - did her death legitimise hysteria as a prerequisite of female creativity? - then thrown away, in a discussion on whether she might have left out more than milk and biscuits for her kids before sticking her head in the oven. Smith ties up all the ends with a conclusion that's both lurid and ludicrous. (It involves a large tank, "I could have been Damien Hirst" diatribes, and the immersion of one of the characters.)

Smith's observational comedy carries the piece when the art-world satire threatens to overwhelm it. His OAPs are passive and taciturn. But the expressions of Mary Wimbush (as Wendy's ailing mother), Gabrielle Hamilton and John Jardine suggest they're compos mentis enough to comment on what's going on - if they weren't so bored and exhausted, principally by the attentions of their carer, Stella. A fount of home-spun practicality, the breezy Susan Brown force-feeds them crisps and jollies them into making cardboard bonnets. But Smith has little sympathy. He's too busy making us laugh at their pitiful second childhoods. With such a talent for acerbic accuracy, Smith should now leave sensationalism alone.

`East': Vaudeville, WC2 (0171 836 9987), to 6 November. `50 Revolutions': Whitehall, SW1 (0171 369 1735), to Saturday. `You Be Ted & I'll Be Sylvia': Hampstead, NW3 (0171 722 9301) to 9 October