Background Green Social Prescribing (GSP) involves referral to nature-based activities to improve health and wellbeing. This project was part of a two-year £5.77m cross-governmental initiative focussing on how systems can be developed to enable the use of nature-based settings and activities to promote wellbeing and improve mental health. The programme funded seven pilot Test and Learn sites across England to scale and embed GSP. The national evaluation was commissioned to understand how the GSP project was implemented at national and local levels, identify learning on how to spread and scale GSP, identify outcomes and value for money of the project for people with mental health needs.

Methods A multi component, mixed methods, realist-informed evaluation comprising quantitative, qualitative and a value for money analysis. Quantitative monitoring data was collected at individual service-user level, and a survey was undertaken utilising GSP providers and NHS Link Workers. The value for money analysis used a wellbeing-adjusted life year approach to estimate the value of benefits to individuals based on improvements in individual life satisfaction following participation in nature-based activities. Qualitative data included key stakeholder interviews (n=118) at two timepoints during the evaluation as a programme theory was developed and tested. This was supplemented with observational data and documentary analysis.

Results The project supported 8,339 people with mental health needs. 57% were from the most socio-economically deprived areas and 21% from ethnic minority populations. There were statistically significant improvements in wellbeing on all 4 dimensions of the ONS4, following nature-based activities and some reduction in depression and anxiety (Hospital Anxiety and Depression Scale). We provide detail from the qualitative findings to highlight contextual issues arising from the quantitative analysis. Social return on investment of the project was estimated to be £2.42 of wellbeing for every £1 invested.

Conclusion This evaluation provides key learning about how to scale and spread Green Social Prescribing and embed it within delivery and the wider social prescribing landscape. Although there are caveats associated with the quantitative data collected, our results showed clear evidence of the positive impact on people’s mental health and wellbeing and the associated value for money of the project. The evaluation highlights the benefits and challenges of embedding large scale social prescribing programmes. Its findings are relevant to other multi partner collaborations delivering interventions at scale.