The family of a young North-East airman who died after lethal nerve gas was tested on him nearly 50 years ago came a step closer to discovering the full truth behind his death today, after a ruling in London's High Court.

Ronald Maddison, 20, of Consett, County Durham, collapsed into a state of asphyxia after a 200mg dose of the deadly nerve agent, Sarin, was dripped onto a patch of uniform taped to his left arm at the Porton Down research centre near Salisbury in May 1953.

It is alleged that Mr Maddison believed he was taking part in experiments to find a cure for the common cold. The original 1953 inquest was held behind closed doors and recorded a verdict of death by misadventure. Mr Maddison's family has fought to unravel the truth of his tragic end ever since.

The Lord Chief Justice, Lord Woolf, sitting with Mrs Justice Hallett, yesterday quashed the original inquest's finding on Leading Aircraftsman Maddison and ordered a new hearing.

After the ruling, one of Mr Maddison's four surviving sisters, Lillias Crake, of Rainsworth, Nottinghamshire, expressed her relief at the result, saying she was "thrilled to bits".

Her husband, John Crake, said the tragedy had hovered over their lives for the past 49 years. "It has always been there because she and Ronald were very close together," he said. "He was a very talented young man, a drummer and musician, not just a name."

The coroner's counsel, Ian Burnett QC, told the High Court that the family felt "that members of the British armed forces may have been used unwittingly as human guinea pigs in tests using some of the most lethal chemical agents known to man".

Police investigated his death after looking into another case stemming from experiments carried out at Porton Down in the 1950's and '60's, with concerns raised that Mr Maddison may not have given his true consent for the experiment to be conducted.

Their findings were later relayed to the Wiltshire and Swindon Coroner, David Masters, who decided to press for a fresh inquest.

Lord Woolf said the High Court would make no findings as to the facts surrounding the death and the way the original inquest was carried out, but ruled it was in the public interest for a new inquest to be convened.

He said there was no dispute that the original coroner was not provided with full information about a previous, similar experiment conducted at the site.

"The previous inquest was held in camera, which meant that Mr Maddison's family never had the opportunity to hear a public investigation into the causes of his death," he said.

"Because the inquest was carried on in camera, the consequence is that they were kept in total ignorance of what was the true situation in respect of their brother's death.

"For these reasons it seems to me that this is a case where the court should quash the inquisition".