This paper examines lay interpretations of lay health worker roles within three UK community-based health promotion projects. It argues that understanding lay health worker roles requires critical analysis of the complex interrelationships between professionals, lay workers and the communities receiving a programme. Findings are presented that are drawn from a qualitative study of lay engagement in public health programme delivery where a key objective was to examine the perspectives of community members with the experience of receiving services delivered by lay health workers. Interviews and focus groups were conducted with 46 programme recipients from three case study projects; a breastfeeding peer support service, a walking for health scheme and a neighbourhood health project. The results show how participants interpreted the function and responsibilities of lay health workers and how those roles provided personalized support and facilitated engagement in group activities. Further insights into community participation processes are provided revealing the potential for active engagement in both formal and informal roles. The paper concludes that social relationships are core to understanding lay health worker programmes and therefore analysis needs to take account of the capacity for community members to move within a spectrum of participation defined by increasing responsibility for others.