The Communist League was the first Trotskyist group in Britain, formed in 1932 by members of the Communist Party of Great Britain in Balham and Tooting in South London, including Harry Wicks, who had been expelled after forming a loose grouping inside the CPGB, known as the Balham Group, later the British Section of the International Left Opposition. They published a monthly newspaper, Red Flag, and a quarterly journal, The Communist.
In 1933, Leon Trotsky suggested the group should enter the Independent Labour Party, but the leadership decided not to. In 1934, a small group led by Denzil Dean Harber did enter the ILP, as the Bolshevik-Leninist Fraction, and formed the core of the Marxist Group which C. L. R. James joined. Slow progress led to more splits, with the formation of the entrist Bolshevik-Leninist Group in the Labour Party.
The Communist League dissolved and its members entered the Labour Party as the Marxist League, led by Harry Wicks. He began working closely with C. L. R. James, by then leader of the Marxist Group, and in 1938 the two merged to form the Revolutionary Socialist League.