The Socialist Labour Party was a socialist political party in the United Kingdom. It was established in 1903 as a splinter from the Social Democratic Federation (SDF) by James Connolly, Neil Maclean and SDF members impressed with the politics of the American socialist Daniel De Leon, a Marxist theoretician and leading figure of the Socialist Labor Party of America. After decades of existence as a tiny organisation, the group was finally disbanded in 1980.