Spy poisoning: OPCW investigators expected in Britain Investigators from the International Organisation for the Prohibition of Chemical Weapons (OPCW) visit Britain to collect samples of the nerve agent used in the poisoning of former double agent Sergei Skripal that plunged relations between London and Moscow into crisis. The investigators will meet officials from the Defence Science and Technology Laboratory at Porton Down, near Salisbury, where the chemical was identified as the Soviet-designed Novichok. IMAGES from Porton Down and Salisbury.