The Communist Party of Britain (CPB) is a communist party in Great Britain which emerged from a dispute between Eurocommunists and Marxist-Leninists in the Communist Party of Great Britain in 1988. It follows Marxist-Leninist theory and supports what it regards as existing socialist states, and has fraternal relationships with the ruling parties in Cuba, China, Laos, and Vietnam. It is affiliated nationally to the Cuba Solidarity Campaign and the Venezuela Solidarity Campaign. It is a member of the International Meeting of Communist and Workers' Parties, together with 117 other political parties. After the fall of the Soviet Union, the party was one of two original British signatories to the Pyongyang Declaration.

The Socialist Workers Party (SWP) is a far-left political party in the United Kingdom. Founded as the Socialist Review Group by supporters of Tony Cliff in 1950, it became the International Socialists in 1962 and the SWP in 1977. The party considers itself to be Trotskyist. Cliff and his followers criticised the Soviet Union and its satellites, calling them state capitalist rather than socialist countries.