[3] Subsequently, Underhill began working as a junior clerk in the party's head office and became vice-chairman in the constituency of Leyton West.
[4] During the Second World War, Underhill refused to fight, citing his socialism, however served in the National Fire Service in London, often acting as a driver.
[3] From 1948, Underhill served as Labour's regional organiser in the West Midlands until 1960, when he was chosen assistant national agent.
[3] On the resignation of Cledwyn Hughes in 1982, Underhill was elected deputy leader of Labour in the House, a post he held until 1989.
[9] He was a founding member of the reformed Association of Professional, Executive, Clerical and Computer Staff and received the union's gold medal.