Sergei Skripal

A former Russian double agent who passed secrets to British intelligence, Skripal, 66, and his daughter Yulia, 33, were found unconscious on a bench outside a shopping centre in the English cathedral city of Salisbury in March, 2018.

They were taken to hospital in a critical condition and British officials said they had been poisoned by Novichok, a group of nerve agents developed by the Soviet military in the 1970s and 1980s.

Russia has denied any role in the poisoning and says Britain is whipping up anti-Russian hysteria.

The chemical “causes a slowing of the heart and restriction of the airways, leading to death by asphyxiation”, said pharmacology expert Prof. Gary Stephens at the University of Reading. “One of the main reasons these agents are developed is because their component parts are not on the banned list.”

(Photograph:AFP)