Eyewitness offers crucial evidence on nerve gas death

The first eyewitness account of the death of a young British serviceman killed in a nerve gas test that went wrong was given yesterday.

The account from an ambulance man is likely to provide crucial evidence at the reopened inquest on Leading Aircraftman Ronnie Maddison, 20, who died in agony from the nerve gas sarin at the Government's top-secret chemical warfare base, Porton Down in Wiltshire, in May 1953.

Mr Maddison's death was shrouded in secrecy at the time and the inquest, held in camera, recorded a verdict of misadventure; the case was closed for nearly 50 years.

But four years ago a group of ex-servicemen, once guinea pigs in the Porton Down experiments, sought to have the whole matter investigated, alleging they took part under false pretences and some later suffered debilitating diseases.

The case of Mr Maddison - the only known death at Porton Down - was raised again, and last year the Lord Woolf, the Lord Chief Justice, ordered another inquest, saying "justice requires these matters are properly investigated".

The inquest, probably before a jury and to last several weeks, will start soon. The testimony of 70-year-old Alfred Thornhill, who 50 years ago was a 19-year-old National Service army ambulance man at Porton Down, could be central to the case.

Mr Thornhill was called to the gas chamber where human tests were conducted on the morning of 6 May 1953 and saw a sight he has never forgotten: Mr Maddison in convulsions, thrashing around on the floor, spewing substances from his mouth. "I had never seen anyone die before and what that lad went through was horrific," Mr Thornhill said. "The skin was vibrating and there was all this terrible stuff coming out of his mouth ... it looked like frogspawn or tapioca."

Like many volunteers before him - many of whom, it is alleged, thought the tests were research into the common cold - Mr Maddison had two pieces of cloth taped on to his arm, on which were put 20 droplets of sarin.Porton Down's official history says it was "a dose already applied to 70 other volunteers without lasting ill effects".

Mr Maddison, however, suffered a violent reaction, and when Mr Thornhill arrived he was surrounded by scientists "with panic in their eyes".

Mr Thornhill took him to the specially cleared medical unit and there, he says Mr Maddison's leg turned blue in front of him. "It started from the ankle and started spreading up his leg," he said. "It was like watching something from outer space."

The next day, Mr Thornhill says, he drove Mr Maddison's body to a mortuary in Salford, being specifically asked to go by back roads. He says a medical officer told him if he ever spoke of what he had seen he would face jail.

But now he is prepared to speak at the reopened inquest, having given a statement to Wiltshire police, who have investigated events at Porton Down for possible offences.

In August the Crown Prosecution Service said there was not enough evidence to bring anyone to court, but the new inquest may give another verdict, such as "unlawful killing".