International systematic reviews suggest an association between alcohol availability and increased alcohol-related harms. Alcohol availability is regulated through separate locally administered licensing systems in England and Scotland, in which local public health teams have a statutory role. The system in Scotland includes a public health objective for licensing. Public health teams engage to varying degrees in licensing matters but no previous study has sought to objectively characterise and measure their activity, examine their effectiveness, or compare practices between Scotland and England. To critically assess the impact and mechanisms of impact of public health team engagement in alcohol premises licensing on alcohol-related harms in England and Scotland. We recruited 39 diverse public health teams in England (n = 27) and Scotland (n = 12). Public health teams more active in licensing were recruited first and then matched to lower-activity public health teams. Using structured interviews (n = 66), documentation analysis, and expert consultation, we developed and applied the Public Health Engagement In Alcohol Licensing (PHIAL) measure to quantify six-monthly activity levels from 2012 to 2019. Time series of PHIAL scores, and health and crime outcomes for each area, were analysed using multivariable negative binomial mixed-effects models to assess correlations between outcome and exposure, with 18-month average PHIAL score as the primary exposure metric. In-depth interviews (n = 53) and a workshop (n = 10) explored public health team approaches and potential mechanisms of impact of alcohol availability interventions with public health team members and licensing stakeholders (local authority licensing officers, managers and lawyers/clerks, police staff with a licensing remit, local elected representatives). Nineteen public health team activity types were assessed in six categories: (1) staffing; (2) reviewing and (3) responding to licence applications; (4) data usage; (5) influencing licensing stakeholders/policy; and (6) public involvement. Usage and intensity of activities and overall approaches varied within and between areas over time, including between Scotland and England. The latter variation could be explained by legal, structural and philosophical differences, including Scotland's public health objective. This objective was felt to legitimise public health considerations and the use of public health data within licensing. Quantitative analysis showed no clear evidence of association between level of public health team activity and the health or crime outcomes examined, using the primary exposure or other metrics (neither change in, nor cumulative, PHIAL scores). Qualitative data suggested that public health team input was valued by many licensing stakeholders, and that alcohol availability may lead to harms by affecting the accessibility, visibility and norms of alcohol consumption, but that the licensing systems have limited power to act in the interests of public health. This study provides no evidence that public health team engagement in local licensing matters was associated with measurable downstream reductions in crime or health harms, in the short term, or over a 7-year follow-up period. The extensive qualitative data suggest that public health team engagement is valued and appears to be slowly reorienting the licensing system to better address health (and other) harms, especially in Scotland, but this will take time. A rise in home drinking, alcohol deliveries, and the inherent inability of the licensing system to reduce - or in the case of online sales, to contain - availability, may explain the null findings and will continue to limit the potential of these licensing systems to address alcohol-related harms. Further analysis could consider the relative success of different public health team approaches in terms of changing alcohol availability and retailing. A key gap relates to the nature and impact of online availability on alcohol consumption, harms and inequalities, alongside development and study of relevant policy options. A national approach to licensing data and oversight would greatly facilitate future studies and public health input to licensing. Our interview data and therefore PHIAL scores may be limited by recall bias where documentary evidence of public health activity was not available, and by possible variability in grading of such activity, though steps were taken to minimise both. The analyses would have benefited from additional data on licensing policies and environmental changes that might have affected availability or harms in the study areas. The study was registered with the Research Registry (researchregistry6162) on 26 October 2020. The study protocol was published in BMC Medical Research Methodology on 6 November 2018. This synopsis presents independent research funded by the National Institute for Health and Care Research (NIHR) Public Health Research programme as award number 15/129/11.