Giles became a communist after witnessing the destruction of the First World War and visiting the Soviet Union in 1925. He joined the Communist Party of Great Britain (CPGB) during the 1926 United Kingdom general strike, and would remain a lifelong member. Later in life, he became the target of anti-communist witch-hunts in the form of slander by politicians and forged leaflets, leading to him temporarily losing his position as president of the NUT. Despite suffering from political persecution, he achieved a considerable influence over British educational policies, directly aiding the formation of British educational reform after WWII, and greatly improving the working conditions of British teachers.