This paper contributes to a more reflexive mode of research on public engagement with science- related issues through studying actors that mediate science-society interactions, their roles and relationships, and the nature and extent of learning and reflexivity, in participatory governance networks. A mapping framework is developed to describe the roles and relations of actors mediating public dialogue on science and technology in the British context. The roles of social scientists, participatory practitioners, scientists, policy makers and other actors in this regard are shown to be complex, ambiguous and fluid, with clear differences evident in the purposes of critical social science and policy-practice. Despite learning and reflexivity being key reasons for public participation, the ways science and policy institutions learn about and learn from public dialogue remain instrumental only, crowding out potentials for reflexive and relational learning. While actors are often highly reflective about public dialogue as individuals this is routinely closed down or instrumentalised at the level of institutions and wider policy discourses, due to ingrained routines, unreflexive science- policy cultures and incumbent power relations. This calls for renewed critical social science research alongside attempts to catalyse more deliberately reflexive learning relating to participatory governance of science and technology, that is situated, interactive, public and anticipatory.