As a complex operation continues to destroy the remainder of Syria's chemical weapons stockpile, how much will we ever know about the supply routes through which the Assad regime acquired the basic ingredients for its arsenal? Vast quantities of chemicals are traded around the world every day, so what chance do we have of controlling their use by rogue states and terrorists? In the first of a new series, Allan Urry reports from the headquarters of the OPCW - the organisation set up to stop the spread of chemical warfare and which is overseeing the removal and destruction of the Syrian weapons. He also investigates the efforts of terrorist groups including Al Qaeda and al Shabab to develop nerve agents of their own; and examines the global attempts to limit the availability of "dual use" chemicals which are essential in the manufacture of every day products from fertilisers to toothpaste but which can also be turned into powerful explosives for use in IEDs and other bombs. Producer: Paul Grant.