Militant, commonly called the Militant tendency, was a Trotskyist entryist group in the British Labour Party, based around the Militant newspaper launched in 1964. According to Michael Crick, its politics were influenced by Karl Marx, Friedrich Engels, Vladimir Lenin, and Leon Trotsky and "virtually nobody else".
In 1975, there was widespread press coverage of a Labour Party report into the entryist tactics of Militant. Between 1975 and 1980, attempts by Reg Underhill and others in the leadership of the Labour Party to expel Militant were rejected by its National Executive Committee, which appointed a Militant member to the position of National Youth Organiser in 1976 after Militant had won control of the party's youth section, the Labour Party Young Socialists.
In 1982, after the Liverpool Labour Party adopted Militant's strategy to set an illegal deficit budget, a Labour Party commission found Militant in contravention of clause II, section 3 of the party's constitution which made political groups with their own "Programme, Principles and Policy for separate and distinctive propaganda" ineligible for affiliation. Militant was proscribed by the Labour Party's National Executive Committee in December 1982, and the following year five members of the Editorial Board of the Militant newspaper were expelled from the Labour Party. At this point, the group claimed to have 4,300 members. Further expulsions of Militant activists followed. Militant policies dominated Liverpool City Council between 1983 and 1987 and the council organised mass opposition to government cuts to the rate support grant. 47 councillors were banned and surcharged. The conduct of the Liverpool council led Neil Kinnock, Labour's then leader, to denounce Militant at the 1985 Party Conference. Eventually Militant's two remaining Labour MPs were prevented from being Labour candidates at the 1992 general election.
Between 1989 and 1991, Militant led the All-Britain Anti-Poll Tax Federation's non-payment campaign against the Community Charge ("poll tax"). In 1991, Militant decided by a large majority to abandon entryism in the Labour Party. Ted Grant, once the group's most important member, was expelled, and his breakaway minority, now known as Socialist Appeal, continued with the entryist strategy. The majority changed its name to Militant Labour, and then in 1997 to the Socialist Party.