A key characteristic of the English and Welsh system of care provision is that the supply function is divided between two types of organisation: the National Health Service (NHS) and local authorities. These inter-organisational and the related inter-professional divides have long been recognised as problematic from a user and carer viewpoint; and various policy changes have attempted to address them. This paper draws on three different research projects to describe practical experiences of user and carer involvement in this context (a) the Evaluation of the 1999 Health Act Section 31 flexibilities encouraging more effective service delivery partnerships between the NHS and local authorities in England; (b) a Baseline Study of Partnership Working and Flexibilities Use in Wales; and (c) the Evaluation of the NHS Changing Workforce Programme, which implemented new ways of working to improve patient care across health and social care in England. In synthesising the studies' findings, the paper also begins to explore relationships between involvement effectiveness and different types of NHS–local authority partnership as they seek to introduce change and deliver more effective services.