According to historians, Britain used poison gas to quell a 1920 tribal uprising in the northern Kurdish town of Kirkuk.

Arguing strongly for the use of mustard gas in 1919, Winston Churchill -- then a secretary of state in Britain's War Office -- said he did not understand the 'squeamishness about the use of gas'.

'I am strongly in favour of using poison gas against uncivilised tribes,' the former British prime minister was quoted in Iraq: From Sumer To Saddam, by Iraqi expert Geoff Simons.