This research was conducted in response to governmental and public concern regarding the escalating use of section 136 of the Mental Health Act (1983) nationally and of the excessive use of police custody as a place of safety in Sussex in particular. A retrospective analysis of all detentions in Sussex during 2012 was combined with qualitative data from 37 people with lived experience of detention, as well as police, National Health Service (NHS) and allied staff and volunteers. Predominantly, police used s136 as suicide prevention (80%) when no other services or help were available. During the period of study (2013–2016), effective joint working strategies, such as the street triage pilot, were able to reduce the overall rates of s136 detentions and to increase access to NHS place of safety suites markedly. Although the research acknowledges idiosyncratic local factors which contribute to the high rate of detentions across Sussex, the results have wider implications for national policy and practice.