Background English local authorities (LAs) have certain powers they can utilise to help them tackle alcohol-related harms. One such power is the Late Night Levy (LNL) which uses a ‘polluter pays’ principle whereby the LA charges alcohol retailers a fee for selling alcohol after midnight. Public health evaluators are increasingly considering how concepts from complexity science and systems thinking might shed light on how interventions can affect health in complex, real world settings such as local alcohol systems. This study aims to explore how the LNL acts as an event within the alcohol system, with a particular emphasis on understanding how the intervention, actors and the system as a whole adapt and co-evolve in response.

Methods We conducted a process evaluation, using a complex systems perspective, in one LA. We included a range of system actors and utilised qualitative data generation methods. We interviewed LNL implementers and alcohol consumers (n=21), conducted observations in pubs and during community-safety patrols (34.5 hours) and reviewed documents on the LNL and the broader system (n=15). We conducted a deductive thematic analysis, applying concepts from systems thinking and complexity science to: 1) describe the system into which the LNL is introduced; and 2) identify emergent system outcomes.

Results The LNL operates within a complex system consisting of diverse actors with competing goals; these include the local political system and statutory functions, the retail sector, the third sector, residents and users of the night-time economy. Early analyses identified a number of system responses stemming from the intervention, which include: 1) retailer adaptation to the levy; 2) new and evolving relationships between retailers, the police, community-safety officers and LA officers; 3) changes in venue management; and 4) the evolution of the intervention itself in response to broader system feedback. These adaptations are hypothesised to affect alcohol-related health and social harms. However, the intervention also interacts with wider system influences on public health, for example local government budgetary constraints during a period of central government cuts.

Discussion Conceptualising the LNL as an event within a complex system allows us to analyse its trajectory as it embeds within, and influences the broader system in which it is located. Further fieldwork and analyses are ongoing and focus on sampling additional system actors and exploring the influence of the vertical systems (e.g. national policy) which shape local responses to alcohol-related harms.

This study is funded by the National Institute for Health Research (NIHR) School for Public Health Research (Grant Reference Number PD-SPH-2015). The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care.