This report is a case study of primary-secondary substitution as an achievable means of reconfiguring health care in London and the UK more generally. It systematically reviews the available local, national and international evidence on the potential for cost-effective primary-secondary substitution of emergency care. The evidence relating to substitution and first contact care is discussed in five categories. They are, the impact of expanding access to primary care; the potential for reorganising general practice; integrated models of primary-secondary care; reorganising the traditional provision of secondary care, and explicitly restricting access to hospital care. The report highlights important gaps in the literature and draws out the implications of the findings for London.