Objective; The study analysed the UK's successful salt reduction policy and seemingly less successful nutrition labelling policy, using theoretical policy frameworks, to explain their evolution and identify lessons for public health practitioners; Methods; Case-studies on nutrition labelling and salt reduction were developed from semi-structured interviews with government, NGO, academic and industry participants recruited through snowball sampling. Process tracing analysis was used to triangulate the data with the grey and published literature, and explore how aspects of the complex processes were explained by the following frameworks: Policy Networks, Punctuated Equilibrium Theory, Multiple Streams Framework, Contextual Interaction Theory, Policy Success Framework and Multi-Level Governance. Analysis and discussion Several high-profile reports attempted to stimulate action on diet and health in the UK during the 1980s. However, government and industry actors only became 'motivated' to act after the 1996 BSE crisis and 'focusing event', which led to the Food Standards Agency's (FSA) establishment in 2000. FSA developed the UK's successful salt reduction programme through a process of cross-sectoral 'negotiated agreements', resulting in reductions in population intakes. By contrast FSA's traffic light nutrition labelling scheme evolved as a battle between public health actors who championed its more equitable performance and a dominant industry group against its "demonization" of foods. Companies adopted a rival Guideline Daily Amount scheme and undermined the national traffic lights scheme by framing it as a "barrier to trade" in EU 'venues', resulting in a formal EU investigation. Nutrition labelling's complexity, including multiple formats and veto opportunities, contributed to its struggles. Transparent monitoring and sanctions were critical to salt reduction's success under the FSA (2000 - 2010), but their absence from the subsequent Responsibility Deal (2011 - 2015), attenuated interpretations of "success" among public health actors. Both policy processes were highly political and public health practitioners would benefit from enhancing their political skills.