If you like your porridge served with lumps of cliché, Simon Mawdsley's prison drama, with its stereotypical lags and sadistic screws, is for you. The inmates are Webby, the semi-psychotic self-taught philosopher and hard man, Doormat who is nice but dopey, Ray the wisecracker and Alan the middle-class loser whose one flirtation with criminality resulted in the messy death of a cocker spaniel and a three-year stretch.

The warders, played by the same quartet of actors with peaked caps and rubber truncheons, are sneering, detached and ultimately thuggish. Mawdsley's play doesn't attempt to break out of the predictable, but his production is good-natured enough to while away a couple of undemanding hours.

Webby, Doormat and Ray have signed up for art classes - though Ray's interest is chiefly in copping an eyeful of the lissom young teacher. But budgetary restraints mean that the “w**k angel” fails to turn up and, in a credulity-straining act of defiance, the men decide to run the class themselves, painting a mural on the prison walls under the guidance of the nervous new arrival Alan. Soon Webby is painting burning prams, baseball bats and razor wire, Doormat his dream home and Ray an image of his fantasy female, while Alan labours on an abstract piece. Before long, word of their endeavours reaches the outside, with the local press and art college sending deputations to their unusual exhibition.

Questions about class, education, artistic ownership and the liberating power of creative expression are gently raised, but Mawdsley is no Lee Hall and this is not The Pitmen Painters. Though the playwright was apparently inspired by a stint with a prison drama group, his writing is too cosy ever to feel remotely authentic and he seems more concerned with easy laughs than politics. “It's symbolic,” says Webby, of his violent daubings. “Symbollocks,” parries Ray.

Still, the cast are likeable, even if Steven Osborne as Webby overdoes the gruff menace, growling and prowling as if auditioning to play an EastEnders villain. But perhaps that's inevitable when he is part of a picture painted with such broad brushstrokes.

Box office: 020-7837 7816. To Sept 20

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