In 1961, the Young family fell ill with a mysterious ailment. They suffered vomiting and excruciating stomach pains for months. The mystery bug spread beyond the household to strike down some of the children’s friends at school.

In November, Winifred Young was on the train to work when she began to hallucinate. She was helped from the train and taken to hospital, where doctors realised that she had ingested the rare poison atropa belladonna.

That morning, Winifred’s brother, Graham, had made her a cup of tea. The drink was so sour that she took only one mouthful before throwing it away.

Their father, Fred, confronted Graham, but Graham blamed his sister, claiming she had been using the family’s teacups to mix shampoo.

Unconvinced, Fred searched Graham’s room, but found nothing incriminating.

Then, on Easter Saturday, 1962, Graham’s stepmother died from poisoning.

Graham was sent to a psychiatrist, who recommended contacting the police, and when he was arrested in May he confessed to the attempted murders of his father, sister and a friend.

Graham was detained under the Mental Health Act in Broadmoor Hospital, an institution for patients with mental disorders who have committed offences. He was diagnosed as suffering from a personality disorder and schizophrenia, and at 14 was Broadmoor’s youngest inmate since 1885.

Graham spent nine years in hospital before he was deemed fully recovered and released.

He began work as a quartermaster at John Hadland Laboratories in Bovingdon, Hertfordshire. His employers received references as part of Graham’s rehabilitation, but were not informed of his past as a convicted poisoner.

Soon after he began work, his foreman, Bob Egle, began to feel unwell. He became so ill that he could no longer work and, soon after, he died.

A sickness swept through John Hadland Laboratories. Mistaken for a virus, it was nicknamed the Bovingdon Bug and several cases were severe enough to require hospitalisation.

A few months after Egle’s death, another of Graham’s workmates, Fred Biggs, grew ill and was admitted to the London National Hospital for Nervous Diseases. After suffering in agony for several weeks, he became Graham's third and final victim.

Once again, Graham had been making tea laced with poison. He poisoned about 70 people over the next few months.

The subsequent investigation into the mysterious illness plaguing the company led to Graham’s arrest in November, 1971. Police found thallium in his pocket as well as a quantity of poison at his home. They also discovered a detailed diary Graham had kept, noting the doses he had administered, their effects, and whether he was going to allow each person to live or die.

At his trial at St Albans Crown Court, Graham pleaded not guilty and claimed the diary was a plan for a novel.

Graham was convicted and sentenced to life in prison. The press dubbed him ‘The Teacup Poisoner’.

He died of a heart condition in his cell at Parkhurst Prison in 1990, one month before his 43rd birthday.

Tragic though the case of Graham Young was, it sparked controversy and led to a review in the way offenders with mental health issues were treated. There had been growing criticism since the 1960s of the holding of offenders with mental disorders.

A committee was set up by the Home Office and the Department of Health and Social Security, and given a wide remit to investigate the current law and propose reforms.

Forensic mental health services were improved with the development of regional secure units in England and Wales. Prior to this there had been only high security hospitals for such offenders.

The review resulted in the Butler Report, which recommended reform of the psychiatric hospital system, of forensic psychiatry and the insanity defence.