John Ross Campbell was a British communist activist and newspaper editor. Campbell was a co-founder of the Communist Party of Great Britain and briefly served as its second leader from July 1928 to July 1929. He is best remembered as the principal in the Campbell Case. In 1924, Campbell was charged under the Incitement to Mutiny Act for an article published in the paper Workers' Weekly. Campbell called on British soldiers to "let it be known that, neither in the class war nor in a military war, will you turn your guns on your fellow workers, but instead will line up with your fellow workers in an attack upon the exploiters and capitalists." He was sentenced to six months in prison.

The Communist Party of Great Britain (CPGB) was the largest communist organisation in Britain and was founded in 1920 through a merger of several smaller Marxist groups. Many miners joined the CPGB in the 1926 general strike. In 1930, the CPGB founded the Daily Worker. In 1936, members of the party were present at the Battle of Cable Street, helping organise resistance against the British Union of Fascists. In the Spanish Civil War, the CPGB worked with the USSR to create the British Battalion of the International Brigades, which party activist Bill Alexander commanded.