Complaints management is an integral component of good clinical governance and an essential contributor to patient safety. Little is known about complaints against health-care professionals (HCPs) in police custodial settings and sexual assault referral centres. This study explored the frequency with which complaints are made against such HCPs working in England, Wales and Northern Ireland. It explored the nature of those complaints and the procedures by which they are investigated. Relevant information was requested from all police services in England, Wales and Northern Ireland; professional regulatory bodies; and the Independent Police Complaints Commission under the Freedom of Information Act (FOIA). Eighty-nine per cent of police services responded to the FOIA request. However, only a minority of these provided detailed information. Many police services cited the provision of health-care services by external providers as the reason for not holding information upon complaints. There was no evidence of any upward trend in the numbers of complaints over the study period. Delayed response to a request for attendance, incivility, medication issues and issues regarding the quality of reports and evidence were amongst the most common types of complaints described. A small number of responders provided copies of the disciplinary procedures used to manage complaints against HCPs. Significant heterogeneity exists in respect of complaints handling procedures across custodial and forensic medical/health-care services and sexual offence examiner services. An opportunity to identify learning for improvement is being missed as a result of the absence of standardised complaints handling procedures.