The world's most powerful nerve agent
Novichok, the nerve agent believed to have been used in the attack on Sergei Skripal (right)and his daughter Yulia, was first developed in the 1970s and 1980s by what was then the Soviet Union.
The name means "newcomer" in Russian, and indicates the fact that when it was developed it marked a major breakthrough in the power of such chemical weapons.
It was by some way the most powerful nerve agent in the world, and it continues to be thought one of the most deadly weapons available.
It works by overriding neurotransmitters in the body and shutting down the way it works. Death can result either through heart failure or suffocation.