["Health Expectations, Volume 29, Issue 2, April 2026. ", "\nABSTRACT\n\nBackground\nSince 2013, local government in England has held statutory responsibility for public health and concurrently faced financial pressures and limited research capacity. The National Institute of Health and Care Research (NIHR) established Public Health Intervention Responsive Studies Teams (PHIRST) to bridge this gap, commissioning rapid, co‐produced evaluations of complex interventions.\n\n\nMain Body\nDrawing on 5 years of PHIRST South Bank experience and ten diverse evaluations, this paper explores what supports and constrains collaborative evaluation in politically responsive, resource‐constrained local systems. Learnings from across evaluations include the dilemmas of balancing timeliness and rigour, the centrality of relationships and relational infrastructure, and the importance of building research and evaluation capacity in local government teams from the outset. We also consider the applicability and limits of existing evaluation frameworks for system‐level interventions.\n\n\nConclusion\nWe argue that collaborative evaluation is both necessary and fragile: dependant on community engagement, adaptive design, balancing of demands, and building of intersectoral relationships.\n"]