BACKGROUND: There is growing evidence for the use of social prescribing as a means to improve the mental health of patients. However, there are gaps in understanding the barriers and enablers faced by General Practitioners (GPs) when engaging in social prescribing for patients with mental health problems. METHODS: This study uses a qualitative approach involving one-to-one interviews with GPs from across the UK. The COM-B model was used to elucidate barriers and enablers, and the Theoretical Domains Framework (TDF) and a Behaviour Change Theory and Techniques tool was used to identify interventions that could address these. RESULTS: GPs recognised the utility of social prescribing in addressing the high levels of psychosocial need they saw in their patient population, and expressed the need to de-medicalise certain patient problems. GPs were driven by a desire to help patients, and so they benefited from regular positive feedback to reinforce the value of their social prescribing referrals. They also discussed the importance of developing more robust evidence on social prescribing, but acknowledged the challenges of conducting rigorous research in community settings. GPs lacked the capacity, and formal training, to effectively engage with community groups for patients with mental health problems. Link workers, when available to GPs, were of fundamental importance in bridging the gap between the GP and community. The formation of trusting relationships was crucial at different points of the social prescribing pathway, with patients needing to trust GPs in order for them to agree to see a link worker or attend a community activity, and GPs requiring a range of strong inter-personal skills in order to gain patients' trust and motivate them. CONCLUSION: This study elucidates the barriers and enablers to social prescribing for patients with mental health problems, from the perspectives of GPs. Recommended interventions include a more systematic feedback structure for GPs and more formal training around social prescribing and developing the relevant inter-personal skills. This study provides insight for GPs and other practice staff, commissioners, managers, providers and community groups, to help design and deliver future social prescribing services.