A FREEZING February night on the bleak Caledonian Road: hover through the fog and filthy air to the premiere of An Animated Macbeth in Pentonville prison. On the face of it, this grim building’s only advantage as a theatrical venue is that warders are allowed to take away everybody’s mobile phone at the door, a system many West End directors must wistfully envy. But actually, a prison has another inbuilt theatrical asset: passion.

This was a truncated Macbeth, an adapted work with neo-Shakespearean collaboration in the form of poems and couplets from inmates across the country; it was performed without set or props, in dreary grey tracksuits and under the unforgiving glare of neon lights in the prison chapel. It took hardly more than an hour. But it was a knockout.

It made your hair stand on end from the first moment when a dozen men flung themselves to the floor and crawled hissing like Gollum around our feet, right through to the corpse-strewn battlefield where a pool of grey tragedy lay twisted on the floor at the shocked Macduff’s feet. Better still, it took Shakespearean language straight into your head and heart in a way that a familiar play sometimes does not.

The chorus, composed of current Pentonville inmates and ex-inmates who have continued to go to the LSW (London Shakespeare Workout), holds the floor throughout: the great speeches and some of the startling inmate writing added to it are spoken by the handful of professional principals, including Lynn Farleigh, but the chorus snarls or hisses individual words in answer: “blood . . . hell . . . knife . . . breast . . . dark . . . hold!” This circle of men play the emotion of the piece: they are the witches and the clowns but also the temptations, the spirits of cruelty conjured by Lady Macbeth, the physical symbols of compulsion, remorse and the mocking, snarling violence in the human heart which — as any prisoner knows — can turn either outwards or inwards. “Hell . . . dark . . . eye of newt . . . dusty death . . .” Suddenly you see exactly why this national group, under their director Bruce Wall and their visionary chair Gayle Hunnicutt, wanted above all to offer Shakespeare’s words to prisoners, rather than in tedious EastEnders vernacular.

“It’s intense, very intense. It carries you,” said one battered-looking lad. It was new and marvellous to him. “I’m going to try and write something. It’s opened up my head.” Others already write: unsettling little poems tagged on to lines like “When I am sometimes absent from your heart . . .” and “This is the very painting of my fear”. You get a sense of men who were often alone, afraid, horrified at themselves and at life, circling trapped in inarticulate cruelty but now freed by nothing more than some 400-year-old words. Acquainted with grief but new to its expression, they fly.

LSW and the actors who support it have, last year alone, been in 52 prisons, done 73 projects with 1,973 inmates and 219 officers.  Their success stories are legion.  They do not vanish when an inmate is released.  Ex-offenders were in this production, back inside for the three evenings and at ease with the professionals.  But even the men who trooped back to their cells for tomorrow and tomorrow and tomorrow were visibly less cribbed and confined.  And so were we, the audience.