Henry Martin (c. 1864–1951), also known as Harry Martin, was a British socialist. Martin was one of the most notable of the impossibilists in the Social Democratic Federation (being expelled in April 1904), and helped found the Socialist Party of Great Britain later that year. A member of its first Executive Committee (1904–1905), Martin was expelled on 8 April 1905 owing to his joining an unemployed rights association. He rejoined the Party on 6 November 1906 and left again, only to rejoin on 19 June 1908. He was then a speaker for the Party (1909–1911), an Executive Committee member (1911) and briefly Lambeth branch secretary (1911) before finally resigning over the WB of Upton Park affair in 1911. The issue at stake was essentially whether socialist MPs should vote for reforms, the diss