The gruesome reality of chemical experiments carried out by the Ministry of Defence at a controversial ‘military science park’ over the course of 50 years has been revealed.

Teenager soldiers and servicemen unwittingly volunteered to be human ‘guinea pigs’ for a series of experiments at Porton Down, in Wiltshire, in the hope of a bit of extra cash.

But the unsuspecting volunteers were exposed to Sarin gas, anthrax and even the Black Death, a new book has revealed.

One victim was left convulsing with ‘terrible stuff coming out of his mouth like frogspawn’; another teenage serviceman believed he had a four-hour conversation with a school-friend who had died years before, after being injected with a brain-incapacitating drug.

Incredibly, thousands of members of the British public were also unknowingly exposed by government scientists who released spores of a ‘plague-like’ bacteria on the London Underground in 1963.

Although considered harmless at the time Bacillus globigii – or BG to use its military moniker – can in fact cause food poisoning, eye infections, and even potentially deadly septicaemia.

But none of the London commuters were ever told of the experiment.

Scientists at Porton Down assured their thousands of military volunteers that they were ‘totally safe’ before exposing them to a series of dangerous experiments.

Despite being turned into ‘guinea pigs’ by their own government, 21,000 servicemen between 1939 and 1989 were only offered token payments, a day off, or even just a free bus pass