The British government introduced the first mandatory national scheme of unemployment insurance in 1911. This required uniform legal definitions to be introduced to govern rights to state benefits. In an unstructured labour market, this process was never straightforward. In analysing how categories were established and specific rights endowed under constantly changing unemployment insurance law, the article witnesses the re-emergence of conventional judgments reflecting earlier distinctions between “deserving” and “undeserving” claimants. Using convention theory, this article thus explores constructions of legitimacy that underpinned claimant categorization, but also the constraints imposed in a liberal political economy on state-sponsored labour market interventions that blocked official influence on the distribution of work. In this respect, British governing conventions have proved long lasting and are reflected in very similar systems of categorization derived from the same type of market judgment that characterizes recent policies governing support for the unemployed.