Ronald Maddison, 20, died after drops of the nerve agent sarin were dabbed on his arm at the Porton Down chemical warfare testing facility in Wiltshire.

An original inquest in 1953 – held in secret on the orders of then Prime Minister Winston Churchill's government – ruled that there was no one to blame for Leading Aircraftman Maddison's death, resulting in a verdict of misadventure.

But his family claimed that he and other forces personnel were duped into taking part in supposedly harmless experiments to find a cure for the common cold.

Yesterday jurors at a reopened inquest in Trowbridge, Wiltshire, took five hours to return their verdict of unlawful killing. The inquest, described by the coroner as "momentous", could now result in legal action by other servicemen and women.

Mr Maddison, an RAF mechanic from Consett, County Durham, was one of many human volunteers involved in tests from 1939 to 1989 at Porton Down – for 85 years the front line of Britain's research into the use of and defence against chemical weapons.

During the hearing lawyers for the Ministry of Defence said all servicemen who underwent chemical experiments at Porton Down were told beforehand what it would involve. After the verdict the Ministry said it did not believe the result had implications for other volunteers.

But lawyers said it could open the door for other service personnel to sue the Ministry, and last night servicemen involved in the tests called for a public inquiry into what happened to them and a public apology.

The 64-day reopened inquest was the second to be held into Mr Maddison's death since 1953.

After years of campaigning, the Operation Antler inquiry into the case was launched by Wiltshire Police in 1999. In 2002 Lord Chief Justice Lord Woolf granted permission for a new inquest, which began in May this year.

After the hearing yesterday, the lawyer for the Maddison family, Alan Care, said: "Sadly Ronald's sister Llias Craik is unable to attend today, but she wishes me to say that after 50 years the family now know how and why Ronnie died and are pleased that the jury's verdict is unlawful killing by the state."

A spokesman for the Ministry of Defence said it would consider the implications of the judgment and would seek legal advice about a judicial review.

Veteran Terry Alderson, 74, from Danby, Whitby, North Yorkshire, was among the former servicemen who attended the hearing. He called for a public inquiry and a full apology from the Government.

"This shows what liars (the MoD) were," he said. "Nobody volunteered for these tests. We were sent in there like sheep. They treated us like human animals and we that are still alive are the lucky ones."

Another veteran, David Dainty, 65, from Bessacarr, Doncaster, was doing National Service with the Army in 1961 when he went to Porton Down. He went to test what he was told was laughing gas in return for the equivalent of a week's extra pay and an extra 48 hours leave.

The effects of the tests raised his suspicions that the gas was something else, but official confirmation he was a guinea pig for sarin only came after Operation Antler began.
Mr Dainty said: "It is not really about compensation. There are some people who are fairly ill, and maybe a little bit of compensation to pay for their healthcare needs would be right. But a public inquiry is what we want and an apology. Those are the top of the list.

"When these things happened, it was a totally different time. Young men in their 20s today would never do what we did. We were in an age of innocence. We didn't ever think our own side would do us harm."

While in his 40s Mr Dainty suffered a brain haemorrhage and believes it may have been the result of the sarin tests.

Also backing calls for an inquiry is Reg Fort, 64, of Hunmanby, North Yorkshire. He suffered repeated collapses of both lungs after sarin and mustard gas were tested on him when he was just 19.

Wiltshire Coroner David Masters described the inquest into Ronald Maddison's death as "momentous".

He added: "All of those, including the family of the deceased, who needed to know how Ronald Maddison died, are now clear in that knowledge".

He said the cause of death returned by the jury was "the application of a chemical warfare nerve agent in a non-therapeutic experiment".

Mr Maddison died at 11am on May 6, 1953, at Porton Down's medical centre, moments after 200mg of sarin was dabbed on to his arm, the jury said. Respiratory failure because of sarin GB toxicity was the medical cause of death.

The use of the nerve agent on Mr Maddison took place after another test resulted in the "near-fatal" poisoning nine days earlier, of another volunteer, Army serviceman James Kelly, the hearing was told in September.

The ex-Army ambulance driver called to help Mr Maddison, Alfred Thornhill, told the jury:

"He was convulsing and foam was coming out of his mouth.

"Then he was taken into the medical centre where there were scientists and medical people.

"They just threw him on to the bed and gave him a big injection.

"It was a terrible atmosphere – they were all panicking.

"They couldn't handle what they were looking at."

A spokesman for Wiltshire Police said after the inquest the policy of the force was not to comment on a coroner's inquest.