BACKGROUND: Contemporary legislative and constitutional developments in the United Kingdom for public health. This article explores these implications. KEY FINDINGS: Examination of the development of parliamentary sovereignty in the United Kingdom shows that, although there is no formal separation of powers, there is a long established convention that legislation should be subject to detailed parliamentary scrutiny, should respect common law, and should be subject to judicial review. This convention has been overturned. Consequently, many recent laws conflict with long-established human rights. Some are unworkable or damaging or both. Public health professionals are being asked to implement poorly thought out laws, against a background of loss of trust. History warns of the danger that public health could be sucked into participation in repressive policies that override the rights of the individual in the apparent interests of the public good. CONCLUSIONS: There is a need for a rebalancing of power in the United Kingdom, both among the three branches of government (executive, legislature, and judiciary) and its constituent parts (England, Scotland, Wales, and Northern Ireland). Constitutional reform is a long-term aim but for now much can be done to hold the executive to account and to be aware of the dangers faced by public health.