The Socialist League was an organisation inside the British Labour Party, which brought together about 3,000 intellectuals who wanted to push the Labour Party outside the National Government (1931-1940) to the left. The organisation was formed in 1932 through a merger between the National ILP Affiliation Committee (NILP) and the Society for Socialist Inquiry and Propaganda (SSIP). The League ceased to exist in 1937.
The Society for Socialist Inquiry and Propaganda was created by G. D. H. Cole in June 1931, and principally consisted of guild socialists, including Frank Horrabin and Bill Mellor. Cole hoped to attract trade unionists, but although Ernest Bevin agreed to become honorary chairman, Arthur Pugh was the only prominent trade unionist to become actively involved.
The National ILP Affiliation Committee was founded by a group of Independent Labour Party (ILP) members who disagreed with their party's decision in 1932 to disaffiliate from the Labour Party. Led by Frank Wise, they entered into negotiations with the SSIP about a merger, which was achieved in October 1932, forming the Socialist League. Wise was chosen as the new league's first chairman; Cole opposed this, hoping that Bevin would take the post. Cole voted against the merger but remained for a time with the League; Ernest Bevin disassociated himself from the new organisation and its activities.
J. T. Murphy was expelled from the Communist Party of Great Britain in 1932 and went on to join the Socialist League. By 1934 he was National Secretary.
Unlike its two predecessors, the League gained affiliation to the Labour Party. Its members included six Labour Members of Parliament: Clement Attlee, Seymour Cocks, Stafford Cripps, David Kirkwood, Neil Maclean and Alfred Salter. It gained great success at the 1932 Labour Party conference, winning votes committing the party to socialist legislation and, in particular, the nationalisation of the Bank of England and joint stock banks.