British military scientists exposed more than 3,100 human "guinea pigs" to potent nerve gases in top-secret chemical warfare tests spanning four decades, according to new figures obtained by the Guardian.

The figures show for the first time the substantial scale of the nerve gas experiments which were carried out on human subjects by the poison gas establishment at Porton Down, Wiltshire.

Porton's total is three times the number of the US, which has also admitted conducting human trials with nerve gases. The most recent tests were carried out 10 years ago, but officials have not ruled out conducting further tests in the future.

Police last month launched the first criminal investigation into the death of 20-year-old airman Ronald Maddison during nerve gas experiments in 1953.

Detectives are also inquiring into allegations that military personnel were tricked into taking part in chemical warfare experiments at Porton Down.

An annual breakdown of the number of human subjects tested with nerve gases, kept secret for many years, shows that Mr Maddison died at the peak of Porton's nerve gas experiments. In the 12 months leading up to his death, 531 men had been exposed to nerve gas. The total had been steadily rising during the previous three years, from 159, to 234, to 384.

With a large pool of human subjects at their disposal, Porton scientists were able to conduct a panoply of tests with a variety of objectives.

Mr Maddison was one of 396 men in a particularly large experiment in which Porton scientists sought to estimate how much nerve gas would kill a man through layers of clothing or on the bare skin.

The deadly nerve gases were originally developed as weapons by the Nazis. Britain and its allies only discovered the extraordinarily powerful new poison gas as the Nazis were being over-run at the end of the second world war. Within two weeks of finding the new weapon, Porton scientists had tested it on humans, in April 1945.

The bulk of Porton's experiments were done in the early years of the Cold War, when Porton scientists worked rapidly to crack the secrets of how the new weapons harmed the human body.

In the first 15 years after the second world war, Porton used 2,644 men in nerve gas experiments, at a time when Britain was actively preparing to manufacture massive quantities of nerve gas to counter the Soviet chemical arsenal.

Many human "guinea pigs" had liquid nerve gas dripped onto their skin, while others breathed in the gas. The doses administered varied, but Porton insists that all the amounts of gas in the trials were "medically safe". Sarin was the main nerve gas used in the experiments, although some trials involved two other nerve gases, tabun and soman.

From the 1960s, the nerve gas tests slowed down. Between 1966 and 1989, 545 human "guinea pigs" were subjected to the gas.

Porton officials say that this was the last time humans were tested with nerve gas. However, they do not rule out the possibility of administering nerve gas to human subjects in the future. At a cost of £3.5m, a new gas chamber was built and opened in 1996, with a projected life of at least 20 years.

The annual breakdown of tests has been collated from figures disclosed to Ken Livingstone MP and declassified documents in the Public Record Office.

Mr Livingstone said: "This is a massive scandal. We need a full public inquiry to get all the facts. The service personnel who were exposed should get all the medical care and compensation which they deserve."

The US government banned all chemical warfare experiments on humans in 1975 after press revelations triggered a public outcry. Until that year, 1,159 military personnel had been exposed by the American military to nerve gas during the Cold War.

Canada is the only other country which has admitted conducting nerve gas tests on humans, saying that a "small number" of experiments ended in 1968.

It is likely that other countries, such as the former Soviet Union, Iraq, and France, which have had considerable poison gas programmes over the years, have tested humans with nerve gas, but details are unconfirmed and sketchy.

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