This article is based on a unique empirical investigation of the contribution that informal childcare – relatives, friends or neighbours looking after children, usually on an unpaid basis – makes in allowing parents to go out to work. There has been little research on either the use of such complementary childcare by parents, or of the carers who undertake it, and this is a review of a two-stage investigation of both. One of the earliest initiatives of the Labour government elected in 1997 was to put a National Childcare Strategy in place. The strategy recognised the importance of childcare both for the development of children and in enabling parents – particularly mothers – to go out to work. To date, however, childcare needs and provision have been assessed almost entirely in terms of formal childcare. A clear understanding of why working parents use complementary childcare (particularly from grandparents) is essential for any childcare policy that hopes to be attuned to what families actually want. The article argues that policy makers, lured by a simplistic vision of economic vitality into adopting a behavioural paradigm from economics – in which parents are assumed to respond to purely financial incentives – are likely to find themselves distracted from important issues of the social well-being of working families with children. Childcare needs are related to dramatic changes in women's labour market participation over recent years, where the largest increase in female employment has been among mothers of children under the age of five. Neither mothers nor fathers may be in a position to provide the desired amount of childcare inside the nuclear household. This situation gives rise to the possibility of a ‘childcare deficit’. In failing to acknowledge and underpin the value which parents place upon complementary forms of childcare, policy makers are in danger of committing themselves to institutional arrangements which may make that deficit worse in the longer term.