People with mental health problems are overrepresented in the criminal justice system and feature disproportionately at all levels of the criminal justice pathway: They are more likely to be arrested than people without a mental health problem for offences of similar severity and are more likely to be victims of crime than the perpetrator. They are also over represented in the prison population and are at risk of poorer outcomes.

In the UK and other countries, there has been a move towards the ‘de-institutionalisation’ of people with mental illness from the 1980s. This has meant that their treatment and support increasingly takes place within the community. This, however, is reliant on the availability of such mental health community and acute services, and in times of a mental health crisis it is the police who are often the first point of professional contact and who function as ‘gatekeepers’ to services more suited to these clients’ needs. It has been estimated that between 20-40% of police time in the UK involves a mental health concern and demand appears to be increasing.

In the prison population, it has been estimated that in excess of 70% of UK prisoners, including both sentenced prisoners and those on remand, have at least one mental health disorder. In addition, around 75% of all UK prisoners have a dual diagnosis of a mental health problem with alcohol or drug misuse, which may further increase the likelihood of coming into contact with the criminal justice system in the first place, but also increases the likelihood of relapse soon after discharge and subsequent re-entry to the criminal justice system.