Abstract Background Public health solutions to substance use harms are of interest across Europe, where the level of health need among detainee populations is broadly consistent. A need for multiagency working is widely recognised, as well as role changes with a view to the police engaging in health generating activity, as part of the wider public health workforce. This qualitative study explores the prospect for a multiagency, public health pathway in an English county district. This involved multiagency working across the community and custody settings. Methods 25 semi-structured interviews with senior and frontline staff of diverse agencies involved in pathway development, including public health, police, treatment providers and the NHS. A ‘frame-critical’ situational analysis sought to understand the strengths, weaknesses, opportunities and threats presented by the pathway. Data were organised into themes. Results Three themes highlighted the challenges and opportunities for addressing substance use harms via multiagency collaboration across the community and custody settings. The themes highlighted how 1) agencies’ shared commitment to public health was unsettled by subtle differences on the meaning of prevention; 2) community police were more accepting of new health activity than custody police; 3) a trade-off impeded a proactive approach: the need for substance worker capacity to support police in the custody suite (a reactive approach) meant that limited community outreach was possible, despite opportunities for preventative community work involving substance workers and community police. Conclusions Public health solutions are challenging to develop in a context of contrasting understandings of ‘public health’, unclear national policy and resource constraints. The design of multiagency public health pathways must be participatory and inclusive to ensure staff buy-in: in particular, new health activities need to align with police staff’s sense of role congruence. Key messages • Multiagency public health collaborations should start by establishing a shared understanding of what ‘public health’ and ‘prevention’ mean. • A long-term perspective on training and motivational alignment (e.g., via feedback) is necessary to implement health-related activity among custody police staff.