BackgroundLocum doctors give practices flexibility to deliver patient services but there are concerns about the impact of locum working on continuity of care, patient safety, team function, and cost.AimTo explore locum working in English general practices, and understand why and where locum doctors were needed and how they were engaged, supported, perceived, and managed.Design and settingAn online survey was sent to 3745 practices.MethodQuantitative responses were analysed using frequency tables,t-tests, and correlations. Free-text responses were analysed using thematic analysis.ResultsIn total, 605 (16.2%) responses were returned between June and December 2021. Practices made frequent use of locums, preferring regular locums familiar with processes and patients. Disadvantages of agency locums included cost, lack of patient familiarity, and impact on continuity of care. Care provided by locums was generally viewed as the same but sometimes worse compared with permanent GPs. Some practices reported that locums did not always perform the full range of duties, resulting in increased workload for other staff. Practices were largely unfamiliar with national guidance for organisations engaging locums, and, although processes such as verifying documentation were conducted, far fewer responders reported providing feedback, support for revalidation, or professional development.ConclusionLocum working is an essential part of English general practice, but this research raises some concerns about the robustness of arrangements for locum working and the impact on quality and safety of care. Further research is needed about the clinical practice and performance of locums, and to explore how locum working can be organised in ways that assure safe and high-quality care.