Mental health is recognised as a part of the ‘core business of policing’. Changes in community mental health services mean that the police constitute the ‘first emergency service’ for people experiencing a mental health crisis. The nature of policing and mental health in England and Wales, however, is complex and challenging. Officers do not have sufficient resources to deal with people with mental health issues (PMHI) or assist individuals in crisis. PMHI who are suspected of an offence can be cautioned, arrested and/ or taken into police custody. Typically involving low level offences, anti-social behaviour or ‘survival crimes’, such arrests are considered to be unnecessary or contributing to the ‘criminalisation of mental illness’. Alternatively, an individual in need of ‘immediate care or control’ can be detained under section 136 of the Mental Health Act (1983). Such individuals are often taken to police custody cells, rather than NHS Mental Health Section 136 suites, due to lack of capacity in the health system.

The economic implications of these police responses are far reaching. A 2007 report estimated that £1.6 billion is spent annually arresting, convicting, imprisoning and supervising people with identified mental health problems. Processing adult offenders with mental health problems through the criminal justice systems has been found to absorb, on average, more resources (including police, court, prison and probation services), with corollary higher costs, than processing those without mental health problems who have committed an equivalent offence. Similarly, treating the physical health issues of patients with a mental health problems has been estimated to impose up to 45% higher costs on the health system than treating those without, even after the cost of treating the mental health issue has been excluded.

Following the Bradley report in 2009, policing and mental health has attracted a significant amount of policy attention. There has been a renewed interest in the potential of interventions to divert PMHI away from the criminal justice system (CJS) and towards community-based services. Successive UK Governments have subsequently invested funds in strategies to support the identification and diversion of PMHI away from the CJS.

Whilst PMHI can be diverted at various stages of the criminal justice pathway, this review focuses on the early stages, before an arrest takes place. A range of policing strategies have been developed to intercept PMHI at this stage and these are known as police pre-arrest/ pre-booking diversion programmes. Such interventions allow police officers to use their discretion to divert individuals suspected of non-violent, low level offences away from the criminal justice system and towards mental health services. Rather than arresting PMHI, law enforcement officers refer or transport individuals to community based facilities.