THE Pentagon may refuse to release documents vital in determining whether an RAF airman was poisoned during an experiment at Porton Down.

The revelation came after the first pre-inquest review into the death of Ronald Maddison 50years ago was opened and adjourned in Tisbury, near Salisbury.

Wiltshire and Swindon coroner David Masters announced two further pre-inquest reviews would be held in July before the actual inquest, which has been set a tentative date of September 30.

Mr Maddison died on May 6, 1953 aged 20 after taking part in what he thought was an experiment to find a cure for the common cold at the Chemical and Biological Establishment, jointly run by the UK, USA and Canada, at Porton Down on Salisbury Plain.

Although an inquest was held shortly after he died, which recorded a verdict of death by misadventure, the Lord Chief Justice, Lord Woolf and Mrs Justice Hallett, ordered a fresh inquest after other airmen complained to Wiltshire police that "volunteers" were duped into taking part in experiments during which they were exposed to the deadly nerve agent Sarin.

Mr Masters said: "I attended meetings at the Pentagon to seek the release of what we have whittled down to 10 documents. The US Defense Department agreed to review this position again all I can tell you is that to assist they have offered extracts from two documents.

"The coroner sets the boundaries of this inquiry and seeks to review the facts fully, fairly and fearlessly. The Ministry of Defence has agreed to downgrade more than 100 protected documents.

"The first inquest into the death of Mr Maddison was held in camera and recorded a verdict of misadventure I can assure his family this will be a transparent inquiry."