Cicero’s maxim salus populi suprema lex est—the health of the people is the highest law—has long held a fascinating and influential place within law and politics, not least given its prominence within John Locke’s Second Treatise on Government. It is also a maxim, sometimes a mantra, that is frequently found within works in public health ethics; a necessarily political field of applied philosophy. The maxim itself contains various points of inherent contestability. These include questions regarding the proper, or best, meaning of ‘salus’. And they include questions regarding the basis and scope of legitimate state action; amongst others, in relation to government intervention that is not based on a positive legal power, or that involves a breach of the law. In this paper, I explore the ideas that emanate from debates on the meaning and legitimate scope of salus populi suprema lex est both against normative and practical understandings of authority. Recognising and relating the discussion to critical discourses regarding the UK government’s legal and policy responses to the coronavirus pandemic, my central concern is to look at the nature of authority of public health laws outside of emergency situations. This includes analysis of approaches to public health law scholarship and practice leading up to the time of the pandemic, as well as appraisals of how the (implied) use of law in response to coronavirus demands open appraisals of the authority claimed then and since of public health laws. The situation demands attention, as the literature well shows, to basic trust in government and fundamental legal principles, such as legality and the rule of law. But it also invites consideration of the merits (or otherwise) of sector-based legislation for questions that reach fundamentally across policies, and of the place of health against devolution arrangements. Legal scholars working in public health must face head on the challenge of addressing where basic legal principles sit within broader structures of principle and power, with open understanding of the consequences of this for the very idea and authority of law itself.