Government social researchers are a group of civil servants who have been overlooked in the existing literature on policy-making in the UK. Their role is particularly intriguing in policy areas relating to environment, food, and energy policy. In these domains, researchers in Science and Technology Studies have argued that policy-makers hold flawed assumptions about citizens’ views and likely actions, contributing to an image of UK policy institutions as overly technocratic and resistant to change. In this context, this thesis aims to understand changes in social research capacity and influence in the Department for Environment, Food and Rural Affairs (DEFRA) and the Department of Energy and Climate Change (DECC) between 2001 and 2015. Based on an analysis of more than 200 documents and 46 interviews with civil servants and external researchers, this thesis illuminates the growth of social research capacity and influence within DEFRA and DECC, since these departments were formed in 2001 and 2008 respectively. The first two empirical chapters (4 & 5) explain how social research capacity expanded within specific institutional, political, and epistemic contexts, through changes in how actors perceived the meanings, roles, and value of social research. It is shown that, contrary to what has been implied by recent literature, DEFRA and DECC are epistemically diverse and dynamic: they house multiple and conflicting epistemic perspectives which are reshaped over time. Moreover, social researchers are committed to performing a ‘challenge function’, whereby they question assumptions, values, and the framing of ideas. Indeed, such challenging has been important in shaping the capacity for social research within these departments. Social researchers’ ‘challenge function’ has also contributed to their gaining greater influence in DEFRA and DECC. Considering policy areas from each department in depth, Chapters 6 & 7 show that social researchers have enabled both ‘single-loop’ and ‘double-loop’ learning. As a result, in both departments social researchers have had some success in encouraging their colleagues to develop and test out policy ideas with the help of empirical research about citizens’ perspectives and everyday lives. While social researchers’ 'challenge function' is a significant policy learning mechanism, it has also been inhibited in various ways within these departments. The thesis concludes that their challenge function could be strengthened if social researchers gain greater representation in the senior civil service and more institutional recognition of their expert knowledge relating to a policy area (besides their skills). Moreover, better interdisciplinary collaboration is needed early on in policy development processes. Such changes have the potential to improve both the effectiveness and democratic legitimacy of policy-making within DEFRA and DECC.