To think of Porridge is to think of Ronnie Barker dispensing lugubrious humour and canny advice while slumped in his cell. And since that late, great comic is readily available on DVD, you have to ask why Fletcher, the jailbird he played, has been resurrected for a theatre tour.

One answer is that Shaun Williamson is almost more plausible as an old lag who has done unlovely things in his time. Certainly, he looks more like a career criminal with a big, tough face that might be a mix of Bill Sikes, Desperate Dan and the John Prescott who slugged the guy who chucked an egg at him. But he also catches Fletcher’s patience, his belief that the way to endure a five-year stretch is to keep your cool while scoring tiny victories over authority. He’s a crafty innocent, a sly subversive, the Good Soldier Schwejk of HMP Slade.

Maybe that vindicates Dick Clement and Ian La Frenais in their decision to write a stage version of their sitcom. Yet they do often sound as if they’re ripping themselves off. From the start, when Fletcher returns to prison and tries to persuade a doctor that his own shoes are medically necessary, old jokes recur. “Are you or have you ever been a practising homosexual?”, “What, with these feet?” “What does he mean by ‘practising homosexual’?” “One who hasn’t got it right yet.” Those exchanges come from the first episode of Porridge.

Still, it’s fun to revisit the Slade of the 1970s. Officer Mackay, here a sadistically cackling Nicholas Lumley, is still trying to impose order on men he despises. His enlightened colleague Barrowclough, here John Conroy, is still being duped. And Gavin McAlinden’s production is as episodic as, well, a TV series. There’s a boxing bout at which each fighter tries to please the other’s backers by throwing the match. We get a glum Christmas, a botched escape, threats from the wing’s Mr Big. Above all, we get the gauche first-time offender, Daniel West’s Godber, doing his best to survive boredom, depression, “the air of defeat and the smell of disinfectant”.

That’s one of several lines that remind you that the writers’ view of prison life was rueful, even serious. When Fletcher tells Godber to keep “a little of who you once were in your head”, he’s speaking for the thousands banged up in Britain. Clement and La Frenais aren’t exactly radicals — but they do value freedom.

Box-office: 024-7655 3055 to Sat, then touring to Jan 16

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