Spender became a member of the Mass Observation movement, taking pictures of daily life in working class communities. His most famous photographs are of the 'Worktown Study'. (Worktown was the Mass Observationist's codename for Bolton). Taken in a period between 1937 and 1940, his photographs cover the full range of Mass-Observation’s interests – politics and elections; religion; street scenes; industrial landscapes; the public house; market scenes; new buildings and developments; observers in action; sport and leisure time; work in the textile mills; on holiday in Blackpool; street hoardings and advertisements. Spender was joined in this project by the artist, Graham Bell.Toward the end of his involvement with Mass Observation, Spender also took on work as a photographer for the recently established, highly successful photographically illustrated magazine Picture Post.