RESUMEN
BACKGROUND: The increase in demand for young people's mental health services has been met by a growth of co-located mental health service provision in the NHS and third sector. This research explores the benefits and challenges of the NHS collaborating with a charity to provide a step-down crisis mental health service for young people in Greater Manchester, and suggests how the collaboration between the NHS and third sector may be improved for future projects. METHODS: Working from a critical realist paradigm, this qualitative case study utilised thematic analysis of 9 in-depth interviews with operational stakeholders from 3 operational layers, to explore insiders' perspectives of the benefits and challenges of collaboration between the NHS and third sector in the context of the 'Safe Zones' initiative. RESULTS: Themes relating to perceived benefits of collaboration were: doing things differently, flexibility, a hybrid approach, shared expertise, and shared learning. These were counterbalanced by perceived challenges: getting the pieces to fit, obtaining a shared vision, geography, lack of referrals, and timing. The importance of effective communication (e.g. of shared vision, standard operating procedures, key performance indicators) was noted as central to addressing challenges and reaping benefits. CONCLUSIONS: NHS and third sector collaboration can yield a range of benefits, some of which can mitigate against the perceived inflexibility and restrictive nature of usual mental health service provision, thereby providing a vehicle for innovation in step-down crisis care for young people.