Veterans of nerve agents experiments at the Wiltshire defence base in the 1950s sat three rows deep at the town hall in Trowbridge, Wiltshire, as David Masters, the coroner, said his inquiry into the death of Ronald Maddison, was unique and would produce two witnesses who had been present with him in the gas chamber at the time of the fatal test.

Outside the court, Mr Maddison's sister, Lillias Craik, 70, whose brother died less than an hour after having his arm exposed to 200 milligrams of sarin nerve agent, said that after half a century of fighting she hoped the truth of how he was killed 51 years ago today would finally emerge.

Mr Masters said some documents produced for the inquest from America would still have to remain secret. This was despite him making personal trips to the Pentagon to ask for disclosure of papers describing the human testing carried out in the 1950s as part of British and American attempts to develop chemical weapons at the beginning of the cold war.

Mr Maddison, a leading aircraft man at RAF Ballykelly in Northern Ireland, had travelled to Porton Down on May 2 1953, the day of the "thrilling Stanley Matthews" FA Cup final between Blackpool and Bolton Wanderers. He was one of thousands of servicemen to volunteer for testing at the base - many, the jury heard, later stated they had been duped into believing they were helping to find a cure for the common cold.

Four days after arriving, Mr Maddison, a fit man from Consett, Co Durham, who loved skating and playing ice hockey, was dead. He had entered a field testing chamber with five other volunteers, all wearing respirators, at 10am on May 6 and was listed in the records as volunteer 745.

"Serge and flannel was tied loosely on a forearm," said Mr Masters. "Pure sarin was drawn up into a pipette and records show that 20 drops, each of 10 milligrams, to a total of 200 milligrams, were placed on the layers of cloth on the inside of the left forearm.

"Ronald Maddison was the fourth of the six to be contaminated at about 10.17am. Maddison was asked how he felt. He said: 'Perfectly well.' But at 10.40am he said he felt 'pretty queer' and was observed to be sweating. He was immediately sent from the chamber accompanied by one of the officers, his respirator and contaminated clothing were removed, and he walked over to a bench in the open air."

Two minutes later an ambulance was called. "One minute later he said he couldn't hear, he was given atrophine sulphate intravenously, then a further injection. It is proba ble that he became unconscious shortly after he said he couldn't hear." He was taken, ashen grey, to the base hospital. "His respiration became irregular, infrequent, and he was gasping, then that finally ceased," said the coroner.

Over the next 2hr 40min doctors gave Mr Maddison several atrophine injections in his heart and muscles, but at 1.30pm resuscitation stopped.

He was the first volunteer to die as a result of testing at Porton Down and all experiments were stopped. But within a year other servicemen were undergoing similar tests.

An inquest was held in secret 10 days after his death and the coroner recorded a verdict of death by misadventure, giving the cause as asphyxiation. Only in the last few years has his family learned that in the weeks before Mr Maddison's death three other servicemen had suffered adverse reactions to the sarin experiments.

The jury was told these in cluded two "serious adverse reactions" in February and April 1953, and "minor adverse reaction" two days before Mr Maddison's death.

For the first time yesterday the coroner's notes from the original inquest were disclosed in public. The hand-written record revealed that one of Porton's scientists, John Rutland, had told the hearing the levels of sarin used in the Maddisontest were "well above the normal limits".

Mr Maddison's father, John, told the coroner at the time, he believed his son was "perfectly happy" to undergo the experiments.

Mr Masters told the jury of 10 that the original inquest verdict was quashed two years ago by the lord chief justice because of the "exceptional" circumstances surrounding the death which were still a matter of public interest today.

This inquest, expected to last eight weeks and hear from 50 witnesses, comes after years of pressure from the Maddison family and the Porton Down veterans to expose what went on there in the 1950s.

Its boundaries will include an examination of whether volunteers were told they were taking part in common cold tests, whether Mr Maddison gave informed consent, and if the scientists knew the dose they were giving the men was potentially lethal.