Socialist Vanguard Group: minutes, 1943-8; reports, from 1929; circulated letters, 1941-2; membership applications; administrative and subject files; Socialist Vanguard / Socialist Commentary, 1934-75; London branch records, 1943-9.
Socialist Union: minutes, 1951-9; membership and financial records; some subject files 1952-9.
Walter Fliess: includes letters to the press, 1960-81; memoir by Geoff Spencer, 1985; printed works by Leonard Nelson.
Society for the Furtherance of Critical Philosophy: financial papers and correspondence relating to the Society's move from Denmark to England, financial and practical affairs during the Second World War, re-registration as an educational trust, 1940-1976. Correspondence includes letters from Minna Specht, 1945 - 1953.