Audiences for stage shows based on popular television series include the devotees of the series as well as general theatre-goers. Porridge probably straddles both types. It's several decades since Ronnie Barker personified the lovable lag Stanley Fletcher in his attempts to get the better of prison officers MacKay and Barrowclough on the screen. Now Shaun Williamson has the chance to break out.

The script for the play is by Dick Clment and Ian La Frenais, writers of the original series. It gives us life in Slade Prison through a sequence of short episodes, beginning as a new intake arrives. It includes Scot McLaren, who's of West Indian descent, naive-but-nice Godber and recidivist Fletcher. There's an extremely good, flexible set by Paul Wills which properly dwarfs the actors within it; laughter here bounces off high brick walls.

Director Gavin McAlinden keeps it all moving, as though to emphasise how static are these active people's surroundings. It's not pure comedy by any means, though none the worse for that, and the performances are uniformly excellent. Daniel West creates a real sense of Godber's longings and frustrations, emphasised by the character's dyslexia, and one would like to think that Slade would see him no more after the end of his sentence.

Also very well characterised is Ryan Winston's McLaren, a dangerous man to encounter inside or outside these walls, albeit one with a redeeming sense of humour. The stick-and-carrot aspects of the warders give Nicholas Lumley as MacKay and John Conroy as Barrowclough some neat moments of interplay. They may be the fall guys, but they are in the end the ones who hold the keys.

Richard Tate, Matt Weyland and Peter Alexander stand out among the other prisoners and the two scenes in which Claire Andreaddis as Fletcher's well-endowed daughter Ingrid appears are a reminder of the life going on, however chaotically, outside. But of course the whole thing depnds on Fletcher himself, and Williamson doesn't disappoint in the part.

He offers a burly presence where the outward jocularity is a well-crafted shell to allow Fletcher to survive in the environment which has confined him, off and on, for so many years. The clue to the character is in the phrase "There are no locked doors in dreams, but they're there when you wake up". It's acceptance and resentment knotted tightly together. And that is what Williamson gives us.