Moral standards

He also said there were "question marks" over experiments carried out from the 1950s to the 1970s in which the eye condition miosis was artificially induced, which he said "might be said by some to have constituted too great a step into the unknown".

But Professor Kennedy said the tests were carried out in "a thorough, painstaking, careful and often ingenious manner" and were "obviously of great importance in assessing military effectiveness".

And he cautioned against judging the researchers involved against the moral standards of today's comparatively peaceful world.

"The work was conducted at Porton in difficult times," he said.

National security

In response to the report, the MoD said in a statement: "These trials must be viewed in the context of the Second World War and the Cold War and their associated pressures.

"The nation was facing a real threat and these trials were essential for national security in that context.

"Much has changed in law and ethics in the half century since many of these experiments and there is a danger in seeking to apply today's standards when those reflect evolution over that period and did not represent the prevailing standards at the relevant time."

It added: "The Ministry of Defence is very grateful to all those whose participation in studies at Porton Down made possible the research to provide safe and effective protection for UK Armed Forces."