This paper places a critical spotlight on the ways in which governance and social responsibility concerning labour standards work in the context of public sector procurement. Supply chains provisioning the public sector, incorporating a vast array of materials used in public services such as education, health, social housing and transportation, have been under‐researched and under‐theorised in the geographical and wider social science literature on Global Production Networks, Global Value Chains and consumption ethics. Against this backdrop, the paper evaluates the emergence of ethical trading programmes involving labour standards in UK public sector sourcing, drawing on examples from the health, higher education, construction and transportation sectors and a methodology combining interviews with participant observation. Findings show that ethical public procurement is shaped, and often constrained, by: the relatively low profile of many materials used in public services, which challenge effective campaigning and advocacy work; the consequent limits to reputational risk for state departments and first‐tier suppliers if labour issues are encountered in their supply chains; and the significant role of EU and UK procurement law, which until 2014 rendered social responsibility in public sector sourcing a legal risk to specify. Through a practice‐orientated approach and adopting the notion of responsibilisation inspired by governmentality perspectives, the paper grasps how these challenges for ethical public procurement are encountered and negotiated by procurement managers and those influencing them in a neoliberal environment. It is shown that ethical sourcing is significantly less advanced in the UK public sector than it is in consumer goods sectors, with implications for social justice in a whole realm of under‐researched global supply chains.