The government has been found guilty of breaching the human rights of a soldier who was exposed to mustard gas testing at Porton Down, Wilts, 40-years-ago.
One test involved sitting in an air-tight cubicle inhaling gas
Thomas Roche, 67, from Lancashire, stopped work in 1988 due to ill health.
He has been fighting for access to his medical records and for details of the experiments ever since.
Human Rights judges unanimously decided the lack of disclosure breached his "right to respect for private and family life".
Mr Roche claimed his health problems were caused by taking part in Ministry of Defence mustard gas and nerve agents experiments in 1962 and 1963.
He was discharged from the army in 1968 and is now registered as an invalid. He suffers from hypertension, bronchitis and asthma.
Awarding him nearly £6,000 damages and £32,000 costs, the judges said there was evidence that uncertainty about the risk to which Mr Roche had been exposed at Porton Down had caused him substantial anxiety and stress.
Mr Roche served in the Royal Engineers between 1954 and 1968.
In the first Porton Down tests he underwent in 1962, he and seven other men were strapped into chairs in an unventilated room while, over a six-hour period, drops of mustard gas were applied to uniform-type material taped to their skin.
In another test in 1963 he was placed in an air-tight cubicle and inhaled gas through a face mask.