An inquest has decided that serviceman Ronald Maddison was killed unlawfully when he took part in MoD experiments at Porton Down more than 50 years ago.
Ronald Maddison died after an experiment at Porton Down
What is Porton Down?
The Defence Science and Technology Laboratory near Salisbury, Wiltshire, is a Ministry of Defence agency which conducts research into chemical and biological defence.
There has been a similar role, under a variety of guises, at Porton Down since 1916.
Initially, the Royal Engineers Experimental Station housed Britain's work on chemical warfare and defence.
Its role changed with the prevailing global mood, but to this day, military volunteers help research into defence against chemical and biological attacks and their effects.
Who was involved in the tests?
Thousands of servicemen and women were involved in the Porton Down Volunteers Programme, which began in 1916.
But it is the period between 1939 and 1989 which came under particular focus, when at least 20,000 volunteers took part in various trials - many during World War II or at the height of the Cold War.
It is during this time that Leading Aircraftman Ronald Maddison attended Porton Down.
When police began investigating his death, hundreds of other volunteers came forward, saying they, too, had suffered after participating in trials there.
Papers released since the police investigation began show that thousands of volunteers took part in a range of trials at Porton Down.
Some - though not all - were administered chemicals, including mustard gas and nerve agents.
The MoD set up a helpline for volunteers to discover exactly what tests they were involved in.
It estimates that up to 3,500 may have taken part in tests involving - but not necessarily being exposed to - nerve agents.
What were the consequences?
Only Mr Maddison is known to have died directly after the tests.
But hundreds of Porton Down veterans believe their subsequent ill health may have been a result of their exposure in trials. And relatives of some who have since died believe the tests may have led to premature deaths. Many others report no ill effects.
The Ministry of Defence arranged for many volunteers to be monitored by the Medical Research Council and a medical team specialising in Gulf War illnesses.
It concluded that there was no evidence linking ill health and the volunteer programme.
What does the MoD say?
It says it co-operated fully with the four-year police investigation into the volunteer testing at Porton Down and has since made available all relevant documents to veterans who were at Porton Down.
It says direct testing of gases and nerve agents on humans is no longer carried out, and points out that it was a very different global climate when Mr Maddison and his contemporaries were there.
It has so far resisted calls for a public inquiry, pointing out that after a lengthy police investigation, lawyers decided there was insufficient evidence to mount a prosecution.