Eye witness: 'Friends, Romans, lifers, lend me your ears' ? Shakespeare plays the nick

'Cry, Havoc! and let slip the dogs of war." With Shakespeare's words ringing in my ears, I surveyed the theatre audience and silently prayed the dogs of war remained unslipped. Half the audience wore maroon sweatpants and sweatshirts; the other half wore blue-striped shirts and jeans. This was not a typical theatrical crowd. But then this was not a typical theatre.

Deep in the bowels of Wandsworth Prison last week, a 19th-century corridor had been converted into a stage, the walls white-washed and special lighting and sound systems put in place. The 60 prisoners from D-wing were watching their fellow inmates – plus two professional actors – performing Julius Caesar.

The Independent on Sunday was given rare permission to enter within Wandsworth's 18ft-high, razor-wire topped walls, to witness last Thursday's performance – part of a theatre project designed to alleviate the unremitting boredom of prison life.

Her Majesty's Prison Wandsworth is an imposing, creepy Victorian jail, which frankly, strikes the fear of God into you. With my security clearance approved, I am led past the sign hanging on the wall declaring the prison's statement of purpose: "We will deal with those prisoners in our care with respect and humanity, while challenging them to reduce the risk of offending on release". Then through a series of thick metal doors, unlocked and locked again, that takes me beyond an inner wall, across a courtyard and down a flight of stairs that leads to the education wing.

The team from Synergy Theatre Project, a company set up to work with offenders and ex-offenders, is preparing for the night's performance. Two of the cast – professional actors Pandora Collin, who plays Portia, and Leroy Liburd, playing Mark Antony – are warming up. The rest of the cast are in their cells and can be brought down only when guards can be found to fetch them – the jail is operating at capacity with 1,500 inmates; guards are in short supply.

I am guided to my seat by Esther Baker, who, with Chris Burton, founded Synergy. She tells me they try to "treat the inmates like actors putting on a play". The actors arrive wearing prison-issue uniforms and about 15 minutes later the rest of the audience follows them in. With D-wing settled down, the play begins with warnings to "Beware the Ides of March" – thank goodness it's July – talk of overthrowing tyranny and only a modicum of heckling. "You should have your Gucci loafers on, mate," shouts one inmate in the direction of a besuited Brutus. When Portia enters, wearing only a candy-striped dressing gown and talk turns to sex, I fear the worst. Lips smack together making kissing noises – at least the inmates like her, I suppose – but it's followed by other inmates, involved in the plot, telling them to keep quiet. The action moves on without a hitch.

We get to the violent bits. "Et tu, Brute?" says Caesar, staring at Brutus and crashing to the floor, stabbed by conspirators, wielding plastic wine goblets. Daggers have been banned. Pindarus, played by Tyrone, a 25-year-old serving, he later tells me, five years for theft, makes a dash for it but is captured by Octavius's guards. "Take him to Wandsworth," shouts the audience.

At the end, the performers are received with glee. It has been a triumph, something for down-at-luck prisoners to get triumphant about. The actors' performances are greeted with near-delirious applause and cheers. Not that the production has been trouble-free. "You don't get any support. The boys will go back to their cells and the warders will say: 'Here come the drama queens'," bemoans Charlotte Gwinner, who not only directed the play and designed the set but also abridged the text so it met with Prison Service approval, "We had a classic example building the set at the weekend. They gave approval for a whole load of tools to be brought in and then one of the governors decided he didn't want any tools in the prison. We had to talk to another governor and eventually we could bring them back in."

Not just from the authorities, either. With rehearsals starting in April, the original inmate earmarked to play Caesar – "a gangster from Brixton" – was fine until the part where he had to die at the hands of Brutus and his co-conspirators. Instead of shuffling off this mortal coil, he kept fighting back. Fortunately for the production, he was transferred to another jail.

In his place stepped Jim Brookhyser, a 32-year-old American, serving a six-year term for possession with intent to supply Ecstasy. Jim's is a bravura performance. "I was unjustly convicted," he confides in me, urging me to publish his full name because, he says, he has nothing to hide. "I find prison just makes me feel worse and have more anti-social thoughts. It's the nature of the beast – locked up in your cell," he says. "But this play has given me something productive to do. It has been a good cathartic release."

Stephen, 34, who plays Brutus, is six months into a three-year term for handling stolen goods. "It's great to work in a team. The negative energy is channelled into something positive," he says. Like most of the cast he is black – representative of the disproportionate number of black people serving time in our jails.

Mick Lydon, a prison officer since 1968, has given the project his full support. "This gives the guys more self-confidence and brings out their talents," he explains.

Mick locks up the doors behind him, gives the all-clear and leads me back to the visitors' entrance. The birds are singing, the sun is still shining and 1,500 men sit in their cells, waiting for lights out.