Dark secrets of controversial lab which used human guinea pigs
More than 20,000 people have been tested on at the top secret lab which is concentrating on gas attack defences
It is one of Britain's most secretive sites, remaining shrouded in mystery for more than 100 years.
But this week Porton Down found itself at the centre of one of the biggest diplomatic crises the UK has faced in recent years.
The top secret defence base in Wiltshire was instrumental in helping identify the nerve agent used to poison a former Russian spy in Salisbury.
Sergei Skripal and his daughter Yulia were poisoned with a weapons grade nerve agent in the city last week, leaving them fighting for their lives in hospital.
And, not only have scientists from the specialist laboratory been at the centre of a clean-up operation following the attack, but its helped identify Russia as the source of the poison.
The 7,000 acre site, near Salisbury, is one of the UK's most secretive and controversial military research facilities and the oldest chemical warfare research installations in the world.
Scientists from Porton were among the first to create biological weapons as well as one of the world's most lethal chemical weapons, but now its main purpose is to support the military and help combat terrorism.
Porton Down opened in 1916 as the War Department Experimental Station for testing chemical weapons during WW1.
Scientists at the lab researched and developed weapons agents used by the British military during the war such as chlorine, mustard gas and phosgene.
After the war the government decided that work should continue at the site and by 1930 it had grown and developed into the Chemical Defence Experimental Station.
During WW2 research concentrated on chemical weapons like nitrogen mustard and nerve agents such as sarin.
It then led to the development of CS - or tear gas- and VX nerve agent in 1952, one of the most lethal substances ever created which results in a painful death.
The base was later named the Chemical Defence Experimental Establishment.
Chemical weapons were tested on site. Scientists built cannisters full of poison gas that could be released by a timer and they also filled shells with it and released them at targets.
But many of the shells failed to explode meaning the fields are still full of the active chemical agents.
Now Porton concentrates on devising defensive measures against gas attacks after its chemical and biological weapons programme was closed down in the 1950s.
On the government's website it says: "To help develop effective medical countermeasures and to test systems, we produce very small quantities of chemical and biological agents.
"They are stored securely and disposed of safely."
Since 1916 more than 20,000 people have taken part in studies at the base.
Porton Down's experiments on humans have been widely criticised as it is alleged some human 'guinea pigs' were duped into taking part in tests.
Tests were carried out on servicemen to try and determine the effects of nerve agents on humans - with one recorded death due to a nerve gas experiment.Read More...