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 (renamed the Morning Star in 1966). 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.
In World War II, the CPGB followed the Comintern position, opposing or supporting the war in line with the involvement of the USSR. By the end of World War II, CPGB membership had nearly tripled and the party reached the height of its popularity. Many key CPGB members served as leaders of Britain's trade union movement, including Jessie Eden, David Ivon Jones, Abraham Lazarus, Ken Gill, Clem Beckett, GCT Giles, Mike Hicks, and Thora Silverthorne.