An inquest into the death of a North-East airman who took part in secret military chemical warfare tests is about to be re-opened after nearly 50 years, the Attorney General said last night.

He has given permission for the case of 20-year-old RAF engineer Ronald Maddison to be reviewed.

Mr Maddison from Consett, County Durham, died after he was allegedly exposed to a 200mg dose of Sarin nerve gas in May 1953 at the Ministry of Defence's Porton Down laboratories in Wiltshire.

The cases of another 100 servicemen and women, who say they were used as guinea pigs in warfare experiments at the Chemical and Biological Defence Establishment, are still being investigated by police.

A spokeswoman for the Attorney General's office said: ''The Attorney General has given HM Coroner for Wiltshire and Swindon authority to apply to the High Court for a fresh inquest into the death of Ronald Maddison at Porton Down in 1953.'' Only the High Court can order a fresh inquest to be held. But, under Section 13 of the Coroners Act 1988, the Attorney General must first give his consent for an application to the court.

The spokeswoman said the inquest was to be reopened on the grounds of emergence of new information which was not available to the coroner in 1953.

Solicitors representing the ex-servicemen claim many were duped into taking part in experiments after being told they were helping find a cure for the common cold.

The inquest would be the first to be re-opened, and supporters hope a verdict of unlawful killing will be considered.

The original inquest into the death of the airman was held on May 16, 1953, in private for reasons of ''national security''.

Detectives have also been examining evidence from servicemen and women who say they took part in experiments with substances including LSD, the hallucinogenic drug.

A number of files have been submitted to the Crown Prosecution Service for consideration in relation to the investigations.

The Ministry of Defence's chemical and biological weapons research centre has tested 3,000 service personnel in human volunteer experiments since 1945.