The number of people detained under the 1983 Mental Health Act has risen significantly in recent years and has recently been the subject of an independent review. Most existing research into the rise in detentions has tended to prioritise the perspectives of psychiatrists and failed to consider the views of Approved Mental Health Professionals (AMHPs), usually social workers, who ultimately determine whether detention is appropriate. This mixed-methods study focused on AMHPs’ views on the reasons behind the rise in detentions and potential solutions. It included a national online survey of AMHPs (n = 160) and semi-structured interviews with six AMHPs within a Community Mental Health Team in England. AMHPs reported that demand for mental health services vastly exceeded supply and, due to inadequate resources, more people were being detained in hospital. AMHPs argued that greater investment in preventative mental health services and ‘low intensity’ support would help to mitigate the impact of social risk factors on mental health; and greater investment in crisis services, including non-medical alternatives to hospital, was required. Such investment at either end of the spectrum was expected to be more effective than changes to the law and lead to better outcomes for mental health service users.