Aim To understand the effects of Nurse Case Managers (NCMs) working in primary care in the English National Health Service (NHS) from multiple perspectives and how this new role impacts on social workers, this paper reports and discusses findings from a multi-level study of the role of NCMs working in primary care in the English NHS. Background Case management as understood by the NHS is equivalent to key-worker type care management as understood by social workers. However, English health and social services are separately organised with different organisational principles; health services are free at the time of need, whereas social services are means-tested and access is restricted. Methods The study included reviews of evaluations and policy, a national survey of nurse case management in Primary Care Trusts (PCTs) and case studies in three purposively selected PCTs. The views and experiences of patients were collected through face-to-face and telephone interviews with 51 older people and their carers, and these experiences are illustrated. In this paper, we further draw on data reporting the views of NCMs and stakeholders from other disciplines and services. Findings The opinions of older people receiving nurse case management reveal the value of high intensity support to individuals with major health and social needs. The NCMs’ clinical expertise, the improved continuity of care they provided and the psychosocial support they offered, were all emphasised by older people or their carers. NCMs substituted for social workers in some cases, when the older person would not have been eligible for publicly funded social care or had declined it. In other cases, they supplemented social services by identifying unmet needs. In a third category of cases, they may have curtailed social services’ involvement by preventing hospital admission and social services’ involvement as a consequence. The implications of this from the viewpoint of other study participants are discussed.