A key feature of modern policing is external oversight of alleged police misconduct. The present paper focuses on the three UK oversight agencies: the Independent Police Complaints Commission (IPCC), the Police Complaints Commissioner for Scotland (PCCS); and the Police Ombudsman for Northern Ireland (PONI). Document analysis and interviews were utilized to highlight the different models of oversight with regard to the balance of responsibility for complaint investigations. The PONI exemplifies a model of regulatory independence that provides a strong challenge to the very limited PCCS model and intermediate IPCC model. An emerging trend was indentified of co-operation between external and internal agency personnel working towards police reform and areas in which oversight agencies can contribute to reform are presented.