This paper is concerned with the issue of substitution between formal and informal care in Britain between 1985 and 2000. This period provides the conditions for a ‘natural experiment’ in social policy. During the late 1980s/early 1990s, there was an increase in long-stay residential care for older people, which came to an end around the mid-1990s. The paper examines whether this increase in formal services led to a decline in informal care, and whether this was subsequently reversed. The focus is on provision of intense informal care by adult children to their older parents, trends in which are identified using General Household Survey data. The paper shows that there was a decline in provision of intense and very intense co-resident care for older parents between 1985 and 1995, which came to an end in the mid-1990s. These trends in intergenerational care were negatively related to changes in long-stay residential care. In particular, controlling for age and disability, there was evidence of substitution between nursing home/hospital care and very intense co-resident care for older parents. A key policy implication is that an expansion of very intense formal services for older people could bring about a decline in very intense intergenerational care. The paper relates these findings to the current debate on reform of the long-term care system in England.