Participants and randomisation
MAY
Eleven contact centres from across England and Scotland were recruited to participate in the study. Randomisation of contact centres to sequences was conducted in May 2019, using computer-generated block randomisation, stratified by centre size (≤ 500 employees versus > 500 employees). Randomisation was conducted by the project statistician, who was fully blinded to the names of the contact centres, and who generated a list of centre numbers showing the sequences that each centre should be allocated to. Centres were contacted by the SUH team approximately three months before the start date to plan for programme delivery or baseline data collection. Prior to this, centres were unaware of when they would start the intervention.We aimed to recruit 27 participants from each centre for the outcome evaluation, and conduct focus groups with 6–8 employees, and interviews with those in relevant managerial positions (main point of contact for the SUH team) for the process evaluation. Sample size calculations and rationale are reported elsewhere [