ackground: Anxiety and depression often coexist in older people. These disorders are often underdiagnosed and undertreated, and are associated with increased use of health and social care services, and raised mortality. Barriers to diagnosis include the reluctance of older people to present to their general practitioner (GP) with mood symptoms because of the stigma they perceive about mental health problems, and because the treatments offered are not acceptable to them. Objectives: To refine a community-based psychosocial intervention for older people with anxiety and/or depression so that it can be delivered by non-traditional providers such, as support workers (SWs), in the third sector. To determine whether or not SWs can be trained to deliver this intervention to older people with anxiety and/or depression. To test procedures and determine if it is feasible to recruit and randomise patients, and to conduct a process evaluation to provide essential information to inform a randomised trial. Design: Three phases, all informed by a patient and public involvement and engagement group. Qualitative work with older people and third-sector providers, plus a consensus group to refine the intervention, training, SW manuals and patient participant materials (phase 1). Recruitment and training of SWs (phase 2). Feasibility study to test recruitment procedures and assess fidelity of delivery of the intervention; and interviews with study participants, SWs and GPs to assess acceptability of the intervention and impact on routine care (phase 3). Setting: North Staffordshire, in collaboration with Age UK North Staffordshire. © Queen’s Printer and Controller of HMSO 2019. This work was produced by Burroughs et al. under the terms of a commissioning contract issued by the Secretary of State for Health and Social Care. This issue may be freely reproduced for the purposes of private research and study and extracts (or indeed, the full report) may be included in professional journals provided that suitable acknowledgement is made and the reproduction is not associated with any form of advertising. Applications for commercial reproduction should be addressed to: NIHR Journals Library, National Institute for Health Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton Science Park, Southampton SO16 7NS, UK. vii ABSTRACT viii Intervention: A psychosocial intervention, comprising one-to-one contact between older people with anxiety and/or depression and a SW employed by Age UK North Staffordshire, based on the principles of behavioural activation (BA), with encouragement to participate in a group activity. Results: Initial qualitative work contributed to refinement of the psychosocial intervention. Recruitment (and retention) of the SWs was possible; the training, support materials and manual were acceptable to them, and they delivered the intervention as intended. Recruitment of practices from which to recruit patients was possible, but the recruitment target (100 patients) was not achieved, with 38 older adults randomised. Retention at 4 months was 86%. The study was not powered to demonstrate differences in outcomes. Older people in the intervention arm found the sessions with SWs acceptable, although signposting to, and attending, groups was not valued by all participants. GPs recognised the need for additional care for older people with anxiety and depression, which they could not provide. Participation in the study did not have an impact on routine care, other than responding to the calls from the study team about risk of self-harm. GPs were not aware of the work done by SWs with patients. Limitations: Target recruitment was not achieved. Conclusions: Support workers recruited from Age UK employees can be recruited and trained to deliver an intervention, based on the principles of BA, to older people with anxiety and/or depression. The training and supervision model used in the study was acceptable to SWs, and the intervention was acceptable to older people. Future work: Further development of recruitment strategies is needed before this intervention can be tested in a fully powered randomised controlled trial. Trial registration: Current Controlled Trials ISRCTN16318986. Funding: This project was funded by the National Institute for Health Research (NIHR) Health Services and Delivery Research programme and will be published in full in Health Services and Delivery Research; Vol. 7, No. 25. See the NIHR Journals Library website for further project information.