In 1914 a chemist called Fritz Haber offered his knowledge to the German Army. He soon began experimenting with chlorine gas to be used in trench warfare.

The Syria Civil Defence said it had responded to "an attack with chlorine gas" and that nine people were affected, including three of its rescue workers, commonly known as the White Helmets.

Islamic State fanatics returning to Britain could be plotting horrifying attacks using chlorine gas which killed thousands of troops during the First World War. The warning has been given by one ...