The Gibbons twins spoke their own language, hated each other, took up arson and wound up in Broadmoor. Perfect stuff for opera, says librettist April de Angelis

The following corrections was printed in the Guardian's Corrections and clarifications column, Monday July 2 2007

Broadmoor was mistakenly described as a prison at one point in the article below. It is a hospital, more particularly a secure psychiatric hospital, as an earlier description in the article made clear.





On June 20 1982, Jennifer and June Gibbons, troubled teenage twins, British-born of Barbadian parentage, each began what were to become 11-year sentences for petty theft and arson at Broadmoor, the secure psychiatric hospital in Berkshire. They were prolific diary-keepers. "Sick. Mental. Psychopathic," June wrote, with characteristic verve. "Imagine how I felt. Me? A mental psychopath? I only heard about things like that in Alfred Hitchcock ..."

The tale of the Gibbons girls is one of sibling rivalry that seemed in danger of turning murderous, featuring a baffling childhood pact of silence that propelled them, via educational exclusion, to become teenage outcasts who responded to dashed literary ambitions and bungled sexual adventures with a life of petty crime that would lead them ultimately to Broadmoor.

Their story had begun 18 years earlier at a drab RAF base in Haverford West, Wales, where their father Aubrey was stationed as a pilot. Gloria, their mother, kept house and looked after the twins and three siblings. Even as babies, Gloria noticed the twins wanted to do everything together - even struggling to be breastfed simultaneously. Other more troubling signs emerged: at school, June and Jennifer weren't speaking, although they were reading and writing fluently. Yet their parents would hear them chattering endlessly to each other while playing with their dolls; it was as if they had distorted their speech into a secret code only they could understand. Surely, Aubrey and Gloria comforted themselves, their twins would grow out of it.

Anne Treherne, an expert on elective mutes, met the twins and became convinced a game was going on: that by secret eye signals Jennifer was stopping June speaking, controlling her as if she were a robot. The twins spooked her colleagues: moving extremely slowly in perfect time, they seemed inhuman, like "zombies", drinking cups of tea or taking off their coats in eerie unity. A head teacher even called Jennifer "evil".

Cathy Arthur, another expert, secretly recorded the twin's private language; playing it back slowly, she discovered it to be everyday English spoken at enormous speed. Equally striking was the strength of will that lay behind their mutual mirroring: they were taken horse-riding in an attempt to encourage individual freedom of movement - but if one fell off, the other would immediately fall off, too.

Errollyn Wallen, a composer, and myself, a librettist, came across their story in Marjorie Wallace's brilliant book, The Silent Twins. Wallace deciphered the reams of their minutely written journals with the aid of a magnifying glass, finally unlocking the secret, passionate outpourings of the twins. What emerges is a very modern British story, with recognisable heroes and villains: parents in denial about the weirdness of their children, local lads who took turns having sex with the twins in a church, befuddled experts, a narrow-minded judge. Not a legendary German saga, to be sure, or the story of a 19th-century Parisian courtesan - but the misunderstood nature of the twins and the deathly struggle for supremacy taking place between them assured us we had enough tormenting passion for an opera.

Jennifer, born 10 minutes after June, imagined her older sister to be cleverer, prettier, more beloved. Jennifer feared she would be left behind. Later, June would write of Jennifer: "She wants us to be equal. There is a murderous gleam in her eye. Dear lord, I am scared of her. She is not normal ... someone is driving her insane. It is me."

This vicious circle would eventually erupt into violence. June writes: "I feel like suicide, but will that help? I have fresh marks on my face to prove how distressing life is becoming with my twin sister. Have I the strength to kill her?" Yet separation was unthinkable. Each pined and took ill without the other. It was as if they were bound by some terrible spell.

The twins were interested in writing, which provided them with some release from their unhappy existence. June wrote:

Here where the traffic roars I think of the country

give me the little things

give me the mountains for the city

the hereafter for the brambles

An old farmhouse for these grey puddings

Give me seagulls for the crows

But once inside Broadmoor, they were treated with high doses of medication that made it difficult for them to concentrate and their passion for poetry and story-writing faded. Living alongside such inmates as Myra Hindley and Peter Sutcliffe, they were bitterly aware of their youth wasting away.

It was the twins' extraordinary creativity that drew us to their bleak chronicle. They always had a rich fantasy life, in which their dolls took on gruesome, dramatic roles; and now these became the seeds of literary authorship. They read prolifically, including the novels of Jane Austen, and enrolled in a correspondence course with the Writing School. The girls were advised "what not to write about", such as lunatics, drug addicts, prostitutes and American settings.

The twins, with unerring instinct, splendidly ignored this advice, producing a novel each; June's Pepsi Cola Addict (the story of a high-school hero seduced by his teacher and sent to a cruel reformatory, now a hot property on eBay) and Jennifer's Discomania (an equally prized tale about a young woman discovering that a local disco incites patrons to acts of insane violence) are written with narrative flair. Gloria could hear the frantic tapping of typewriters deep into the night. June wrote to the publishers at New Horizon, who had accepted her book on a vanity publishing basis, explaining that she didn't have the money but hoped that eventually royalties would cover the cost. If not, she wrote to them, "then ring the police and I will gladly be arrested". Eventually, the twins managed to strike a deal.

Authorship did not bring the expected results. This plan, like so many of the twin's strategies to break free and make an exciting life for themselves, failed. These two girls were full of frustration and the desire for self-expression, struggling to find an identity in a world, which, in their words, considered them "black and daft". New feelings, longings for sex and love, flooded them. And they must have looked weird, struggling with bottles of brandy and extravagant wigs, binoculars swinging from their necks as they went hunting the attractive American brothers whose father worked on the base. But losing their virginity in a church in an act of double folly did not bring the escape they had hoped for.

June reflects: "I have no feelings for sex. I think it's mean and cruel. I just lie back and let it happen. I want romance and emotional attachment; boys just use my body." As romance failed them and no jobs materialised, cut off from their peers, bored, they sought thrills in crime. June writes: "A lousy day. Broke into Portfield special school, nicked a few Jackie mags. Really fantastic. Why do this? No friends. Nothing else to do. Nothing to fill the cold hour."

If they couldn't be famous writers, they'd be famous criminals. They decided to burn down a tractor shed. They were caught. Once inside the criminal justice system, when their history of "silence" was taken into consideration, they were pronounced to have severe personality disorders, labelled psychopathic and handed an indeterminate sentence, to be released only after significant improvement of their condition. Their bitter struggle intensified in the confines of Broadmoor. The day of their eventual release, 11 years later, brought another extraordinary event: Jennifer's death. She fell ill on the bus that drove them away from the prison and died that night in hospital. Sudden inflammation of the heart was given as the reason, but there was no evidence of drugs or poison, and no cause of death has ever been established.

Wallace believes that, during their stay in hospital, they began to believe that in order for one of them to be free the other must die.

For Errollyn and I, it is the transcendent qualities in the twins - their imagination, guts, talent and humour pitted against the confining effect of each other and a world that was at best indifferent and at worst hostile - that makes their struggle, with its tragic denouement, a gripping story that we wanted to tell in music and words. The story of the twins is also a love story: can't live with her, can't live without her. Why make it an opera? Why sing it? Because the drama requires music to take us to a place words can't reach alone. The twins, with their ceaseless fight to the death and their love that knew no bounds, are perfect opera material.

"You are me," Jennifer would intone to June as June screamed back, "I'm June, June." I put this exchange into the libretto; simple words that suggest big musical emotions. What was always compelling to me were the elements of magic in their story - the unexplained nature of their pact of silence, the uncanny effect they had on those who encountered them and Jennifer's mysterious death.

It seemed inappropriate to speak for the twins - so in the libretto only words they spoke or wrote are used, as well as occasionally an imagined reconstruction of their invented language.

The glorious and sad paradox of the silent twins is that they weren't silent at all: they were adventurous and passionate communicators who, in novels, journals and poetry, recorded their responses to the world with perception and originality. It's just a shame there was no one there to hear them. Another reason to celebrate them loud and clear in music.

The twins get under your skin. I had a text from Errollyn one day saying: "Jennifer is dead." I went icy cold. Jennifer who? Then I realised Errollyn was setting the denouement. Afterwards she said: "I'd been dreading it, because I knew it would be so sad. When you write the music, you have to get right inside the twins - but I steeled myself and did it. I shed some tears".

· The Silent Twins is at the Almeida, London, July 5-16. Box office: 020-7359 4404.