This paper explores the relationship between social mobility and class formation in a working-class industrial suburb. By establishing the degree of class closure in three periods we can identify the relationship between the country's political history, dominated by the rise of a left-wing Labour Party, and the changing levels of closure. Labour established itself during a period of low mobility then stalled when mobility increased sharply in the 1920s. Comparison with the mobility rates for cities in other countries allows further analysis of the relationship between social structure and political behaviour. Our evidence indicates that voters were not unconscious of the shifting patterns of class rigidity.