Chief medical officers in the United Kingdom: maintaining 'independence' inside government.

Background: The Chief Medical Officer (CMO), one of the UK's most senior public health leadership roles, was crucial in supporting policymakers in responding to COVID-19. Yet, there exist only a handful of (largely historical) accounts of the role in England. This article is the first to empirically examine how the scope, focus and boundaries of the CMO role vary over time across the four UK nations, including during public health emergencies.

Methods: We undertook semi-structured interviews with 10 current and former CMOs/Deputy CMOs in the four UK nations and analysed relevant documents.

Findings: The CMO role is not clearly defined in contemporary UK legislation and is instead shaped by iterative policies, incumbent preferences, and organizational needs, leading to variation over time and between nations. Nonetheless, most participants framed the role as primarily providing 'independent' advice to government despite being senior civil servants who, in communicating with the public, sometimes speak 'on behalf' of government.

Conclusions: The flexibility of UK CMO roles allows for responsive adaption but poses risks for how well these roles are understood. A potential tension between providing 'independent' policy advice and a need to publicly communicate government policies and guidelines may be exacerbated in emergency contexts.