BackgroundSubstantial policy, communication and operational gaps exist between mental health services and the police for individuals with enduring mental health needs.AimsTo map and cost pathways through mental health and police services, and to model the cost impact of implementing key policy recommendations.MethodWithin a case-linkage study, we estimated 1-year individual-level healthcare and policing costs. Using decision modelling, we then estimated the potential impact on costs of three recommended service enhancements: street triage, Mental Health Act assessments for all Section 136 detainees and outreach custody link workers.ResultsUnder current care, average 1-year mental health and police costs were £10 812 and £4552 per individual respectively (n = 55). The cost per police incident was £522. Models suggested that each service enhancement would alter per incident costs by between −8% and +6%.ConclusionsRecommended enhancements to care pathways only marginally increase individual-level costs.