Sustainable return-to-work in large organisations: feasibility of a multi-level cluster-randomised controlled trial

Background: Long-term sickness absence is a growing public health concern in the UK, yet few workplace-based interventions address both health and work factors needed to support sustainable return-to-work. This study assessed the feasibility of delivering and evaluating a multi-component return-to-work intervention to inform a fully powered trial. Methods: We conducted a two-arm, cluster randomised controlled feasibility trial in large organisations (≥600 employees) across NHS, public services, higher education, and private sector in Yorkshire and Humberside, UK. Nine clusters participated, including 91 senior leaders and HR professionals (intervention only), 112 workers (43 intervention, 69 control), and 83 managers (20 intervention, 63 control). Eligible workers were on long-term sick leave (15–42 days) for mental or physical health conditions. The IGLOo intervention comprised three phases: (1) e-learning for senior leaders and HR; (2) and (3) mirrored six-step online toolkits for workers and line managers during sick leave and post-return to work. Feasibility outcomes included recruitment, retention, intervention completion, acceptability, and usability assessed using predefined stop–go traffic light criteria. Secondary outcomes (collected at baseline and 3, 6, 9, and 12 months) included sick leave duration, sustained work participation, mental health, quality of life, workplace support, and communication Web analytics, qualitative interviews and an organisational survey explored engagement, implementation and contextual factors. Results Retention, acceptability, and usability met green feasibility thresholds. Intervention completion met amber thresholds. However, recruitment of workers and managers met red thresholds. Qualitative findings identified mechanisms supporting sustainable return-to-work including improved confidence, communication and job-crafting; and highlighted organisational factors (e.g. workload, restructuring, managerial capability) that shaped feasibility. Preliminary exploratory findings indicated that workers in the intervention group took longer to return to work but were more likely to return and remain in work compared with controls. Conclusions Findings indicate that the IGLOo intervention is acceptable and usable, with promising indications for supporting sustainable return-to-work. Recruitment challenges and contextual barriers suggest refinements are required before progressing to a fully powered trial. A future trial should prioritise improved recruitment strategies and consider organisational readiness to implement multi-level return-to-work support. Trial registration number ISRCTN11788559, registered on 6 ^th October 2022 (prospectively registered))