The following correction was printed in the Observer's For the record column, Sunday October 5 2003





Like most 19-year-olds, Alfred Thornhill had never seen anybody die. When the fresh-faced trainee engineer from Salford answered his call for National Service, he thought he could handle anything.

Dispatched to the ambulance service, the self-confident teenager arrived for a month-long posting at Porton Down, the Government's top-secret chemical weapons laboratory in Wiltshire. He was proud to be doing his bit for his country.

But nothing could have prepared the young Mancunian for the horrific events he witnessed on a May morning in 1953. Answering an emergency call, he witnessed scenes which would haunt him for half a century and thrust him to the centre of an inquiry into one of the darkest hours of British military history.

Until today Thornhill - now a 70-year-old pensioner - has never spoken publicly about what he saw. He feared the Ministry of Defence would send him to prison.

He has now broken his silence to tell of the day he arrived at Porton Down's gas chamber and saw the convulsing body of 20-year-old Ronald Maddison thrashing around on the floor, spewing substances from his mouth.

Thornhill's eyewitness testimony will form a key plank of the reopened inquest into Maddison's death, which is due to be heard in the next few weeks.

Maddison, an RAF engineer from County Durham, had been used as a human guinea pig by MoD scientists experimenting on the lethal nerve gas sarin. Like hundreds of others from the armed forces, Maddison had volunteered for the trials, believing he was going to Porton Down to take part in some 'mild' experiments to find a cure for the common cold. Instead, by dropping sarin onto Maddison's skin, they used him to help determine the dosage of the lethal nerve agents.

Thornhill's accounts of the agonising last hours of Maddison's life shines a light into the murky past of this secretive establishment and the shocking experiments carried out on volunteers. Hundreds are suspected of dying prematurely or going on to develop illnesses such as cancer, motor neurone disease and Parkinson's. Despite the grief and fury of survivors and their families, over the decades successive Governments have sought to bury the scandal. But Thornhill's testimony could change all that.

'I had never seen anyone die before and what that lad went through was absolutely horrific... it was awful,' he said. 'It was like he was being electrocuted, his whole body was convulsing. I have seen somebody suffer an epileptic fit, but you have never seen anything like what happened to that lad... the skin was vibrating and there was all this terrible stuff coming out of his mouth... it looked like frogspawn or tapioca.'

Thornhill recalls a number of scientists standing around Maddison. 'You could see the panic in their eyes - one guy looked as if he was trying to hold his head down. There were four of us who picked him off the floor and put him in the back of the ambulance. He was still having these violent convulsions and we drove him to the medical unit at Porton.'

By the time he reached the unit, it had been cleared of other casualties and there were men in white coats standing around a bed.

Thornhill was told to carry Maddison over and it was then that the young ambulance driver saw a second image that would haunt him for decades.

'I saw his leg rise up from the bed and I saw his skin begin turning blue. It started from the ankle and started spreading up his leg. It was like watching somebody pouring a blue liquid into a glass, it just began filling up. I was standing by the bed gawping. It was like watching something from outer space and then one of the doctors produced the biggest needle I had ever seen. It was the size of a bicycle pump and went down onto the lad's body. The sister saw me gawping and told me to get out.'

The next day Thornhill was 'devastated' when he was told by a medical officer that the young man had died. He recalls the whole medical unit stinking of Dettol as if it had been sprayed everywhere to decontaminate the rooms. Thornhill was asked to drive the body to the mortuary at Salisbury General Hospital and instructed to take the back roads.

At the time, Thornhill was suspicious of what had happened and why he was told to take such a strange route to the hospital, but he simply followed orders.

'There was a lot of talk among the squaddies about nerve gas and mustard gas and the like, but nobody really knew what was going on. In those days you trusted the authorities and didn't ask too many questions. You kept yourself to yourself.'

There was another reason why Thornhill kept quiet. 'I was called into an office and read the riot act by a medical officer. He made me sign something and told me if I ever spoke a word about what I saw at Porton Down I would be sent to prison. I was frightened and didn't want to go to jail, so I didn't tell any of the other lads what I had seen.'

Over the years, Thornhill has had frequent flashbacks of the terrible events he witnessed, but has never mentioned them outside his immediate family. 'I used to see things on the news and on TV that used to bring it all back to me. I remember seeing the news about Saddam Hussein gassing the Kurds and I couldn't stop thinking about that young lad.'

For 50 years, Thornhill found it difficult to stop wondering who the dying man was. 'I noticed his blue RAF trousers under the blue boiler suit, but that's all I ever never knew about him. I thought he might be married and his wife or parents would want to know what happened and that there was somebody with him when he died. I was recently engaged and I would have hoped somebody would have done the same for me.'

Yet it was only this summer when he heard a report on a local Manchester radio station about a police inquiry into the death of the RAF engineer Ronald Maddison at Porton Down, that it all fitted into place. 'I stopped in my tracks when I heard it. I knew that was it him, that it was Maddison. It was the right date, he was in the RAF and they said it was the only person who had died at Porton.'

Thornhill telephoned the Wiltshire police who were conducting the inquiry and a team travelled to Manchester the next day to interview him. He gave them a nine-page statement detailing all he knew and saw at Porton Down during his time there. An original MoD inquest was held in secret in 1953 and recorded a verdict of death by misadventure.

Although the police inquiry into events at Porton Down found insufficient evidence to mount a criminal prosecution, their findings were passed to Lord Chief Justice Woolf who ruled that the inquest must be reopened. Lawyers for Maddison's family and the hundreds of other volunteers who have suffered subsequent illnesses are hoping for a verdict of 'unlawful killing'.

Thornhill now wants to meet Maddison's family so he can talk to them about what he saw. 'What that lad went through was horrendous, it shouldn't have been allowed to happen to anybody. We talk about Saddam Hussein gassing his own people but what we did at Porton Down was the same... I want his family to have some justice.'

With Thornhill now ready to speak out 50 years later, Maddison's family might finally be able to get just that.



Race to test a Cold War killer



Porton Down was established as a research centre on the edge of Salisbury Plain in 1916, to help Britain catch up with German chemical weapons technology.

By the time Alfred Thornhill was an ambulance driver there in 1953, British intelligence believed the Soviets were stockpiling nerve agents, such as sarin, which could kill instantly or cause paralysis, convulsions and breathing difficulties. Scientists at Porton Down wanted to know the precise doses to cause such symptoms.

From 1945 more than 3,000 men were sent into the gas chamber; various amounts of liquid nerve gas were dripped by pipette onto their arms. Many believed they were helping to find a cure for the common cold.

Ronald Maddison died 45 minutes after 200mg of the deadly nerve agent sarin was dripped onto a patch of uniform on his arm.The coroner's report was never released but Lord Chief Justice Woolf has now ordered a fresh inquest.

antony.barnett@observer.co.uk