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 mirrored the Soviet 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 most notably Jessie Eden, David Ivon Jones, Abraham Lazarus, Ken Gill, Clem Beckett, GCT Giles, Mike Hicks, and Thora Silverthorne.
The CPGB's position on racial equality and anti-colonialism attracted many black activists to the party, including Trevor Carter, Charlie Hutchison, Dorothy Kuya, Billy Strachan, Peter Blackman, George Powe, Henry Gunter, Len Johnson, and Claudia Jones, who founded London's Notting Hill Carnival. In 1956, the CPGB experienced a significant loss of members due to its support of the Soviet military intervention in Hungary. In the 1960s, CPGB activists supported Vietnamese communists fighting in the Vietnam War. In 1984, the leader of the CPGB's youth wing, Mark Ashton, founded Lesbians and Gays Support the Miners.
From 1956 until the late 1970s, the party was funded by the Soviet Union. After the dissolution of the Soviet Union in 1991, the party's Eurocommunist leadership disbanded the party, establishing the Democratic Left. In 1988 the anti-Eurocommunist faction launched the Communist Party of Britain, which still exists today.