Objective: To investigate the profiles of advanced clinical practitioners (ACPs) in the allied health professions (AHPs) and their skills, attributes, experiences and involvement in new models of care. Methods: A 2 phase, cross sectional, mixed method survey of AHP ACPs across London was conducted in 2018-2019. Online questionnaires were completed by 127 AHP ACPs and then semi-structured interviews were conducted with 15 AHP ACPs. Results: The survey results gave a comprehensive overview of the attributes of AHPs in ACP roles across London. There was considerable variability between role titles, types and levels of qualification, and evolution of the roles. The respondents predominately worked in clinical practice, and less frequently in other ACP domains (research, leadership and management, education). The interview findings provided in-depth insights into the AHP ACP roles within four themes: being advanced, career pathways, outcomes of the advanced practitioner role and influencing and transforming. The "Being advanced" theme highlighted that expert practice comprised confident and autonomous practice, leadership, and applying specialist and expert decision-making skills. "Career pathways" highlighted the diversity within the participants' roles, titles, career opportunities and development. In the "Outcomes of the advanced clinical practitioner role" theme, the ACPs described their services as prompter, more accessible and providing an improved patient journey. The "Influencing and transforming" theme highlighted networking and dissemination and ideas for innovation, influencing and transforming services. Conclusion: This is the first comprehensive profile of ACP roles across AHPs and indicates that these roles are already having a positive impact on healthcare services and supporting new models of care. However, establishing the necessary infrastructure, standardization and governance for ACP roles across sectors, along with the career pathways, funding, sustainability and education, could increase impact in the future.