More the 30,000 of the darts could be stored in cluster bombs, which could be dropped onto enemy troops from an aircraft at 3,000ft, according to the file entitled Research Into Use Of Anthrax And Other Poisons For Biological Warfare.

Death of a target would occur in 30 minutes if the darts were not removed quickly.

In chilling detail, experts list the side-effects of the specially concocted – but unidentified – poison.

When tested on sheep the animals were ‘rendered helpless’ within one to five minutes and were dead within half an hour. Effects included profuse salivation and sweating, acute defecation and retching.