What is Alleged British use of chemical weapons in Mesopotamia in 1920?

It has been alleged that the British used chemical weapons in Mesopotamia in 1920, during the Iraqi revolt , in the period of the British Mandate over Mesopotamia. Use of tear gas and lethal poison gas against Iraqi rebels was considered, and the use of tear gas was promoted by Winston Churchill, head of the War Office, as he argued it would frighten Iraqi rebels and cause them to flee while not actually killing anyone nor leaving serious or lasting effects on those caught in the tear gas and that the use of non-lethal tear gas was an overall better solution than the bombing campaign which failed to quell resistance to British control in Iraq. Practical difficulties prevented its use rather than any moral inhibitions.