Introduction: The rapidly increasing prevalence of long-COVID (LC), the multisystem complexity of the condition and high patient symptom burden, necessitated an immediate need to develop new clinics for assessment and management. This article reports on the rapid implementation of a reactive and responsive LC care pathway.  We mapped patients’ journey through this pathway, identifying the services that were activated according to prevalent symptoms, and assessed the barriers and facilitators to its implementation and delivery, from the perspective of health care professionals (HCPs) and LC patients using the Theoretical Domains Framework (TDF).   Methods: Mixed methods study, including retrospective quantitative cross-sectional analysis of patient data and semi-structured qualitative interviews. One hundred and sixteen patients who attended long-COVID clinic in Hertfordshire, UK, in the first 5 months of its existence, consented for their data to be analysed for the quantitative study. Six HCPs and five patients participated in semi-structured interviews.   Results: Patients were referred into the service an average of 5.75 months post initial COVID-19 infection. 82% of patients required onward referral to other HCPs, most commonly pulmonary rehabilitation, chronic fatigue specialists, and the specialist COVID-19 Rehab general practitioner embedded within the service. Patients reported having rehabilitation needs, moderate depression and anxiety, and difficulties performing usual activities of daily living at point of care. The TDF domains most relevant to the implementation of the LC pathway were beliefs about capabilities, environmental context and resources, knowledge, and reinforcement. Discussion: Our study provides novel insight into the development of a reactive multidisciplinary care pathway. Key drivers for successful implementation of LC services were identified, such as leadership, multidisciplinary teamwork, transferable skills, and knowledge exchange. Barriers to rapid set up of the service included funding constraints and the rapid evolution of an emergency context.

HM received funding for a long-COVID GP Fellowship, to undertake clinical work and research, from NHS East and North Hertfordshire CCG. HM's role within the study was funded by the LOCOMOTION study funding (National Institute for Health and Care Research, grant ref: COV-LT2-0016). HM received payment and travel expenses for long-COVID-related presentations and expert opinion. The remaining authors have declared that no competing interests exist.

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Ethical approval for the study was obtained through Health Research Authority (HRA) and Health and Care Research Wales (HCRW) London - Camden & Kings Cross Research Ethics Committee (REC reference: 21/PR/0987). All participants provided informed consent prior to participating in the study. University of Hertfordshire and institutional ethics guidelines were followed.

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