Career
Neumann had previously been very active in the Social Democratic Federation, being a public speaker for that party and secretary of its Chelsea & Fulham branch in 1897. Neumann was a well-known early Impossibilist, being a victim of the expulsions of April 1904 which led to the foundation of the Socialist Party of Great Britain in June. From 1904 to 1909 he was on the Executive Committee and from 1909 to 1911 was Treasurer.
Herbert Morrison described his encounters with Neumann in his 1960 autobiography as follows:
Neumann resigned on 12 September 1911.
He was presumably repatriated to Germany at the end of the war and is reputed to have died in the Spartacist uprising of January 1919.