This thesis aims to explore aspects of the democratisation of science within the UK. It does this through focusing on the analytic-deliberative practice of participatory risk appraisal (PRA), which emphasises the active involvement of citizens and stakeholders in the framing, assessing, and evaluation stages of complex and uncertain environmental risk policy processes. This was achieved by following professional actors (comprising process-experts, scientific-experts, and decision-makers) through networks currently building around PRA practice across the UK more generally, and in the area of radioactive waste specifically. Analysis shows that professional actors can be seen to belong to an epistemic community comprised of a core group of process experts (researchers and participatory practitioners). This community is in an early stage of development at present and characterised by significant fragmentation between specific actor groupings within it. This coupled with intensely competitive relations between actors means that the community is not learning as effectively as it might. Unless the community makes a more concerted effort to faithfully represent a learning community its potential to democratise science within the UK will remain limited. Closer analysis within the area of radioactive waste provides evidence that community members are influencing the beliefs of decision-making institutions, and enhancing scientific reflexivity, in geographically localised and institutionally specific instances. They have played a central role in bringing about a shift away from a technocratic mode of decision-making prior to 1997, towards one that is more democratic. A key indication of this democratisation is the significant degree to which citizens are being involved in processes of extended peer review, and possibly contributing extended facts, in the framing stage of decision processes within the area. A final insight of the thesis is that community members possess shared understandings about effective PRA. Fifteen shared principles of effective practice are identified in relation four themes: the overall shape of the analytic-deliberative process; the role of science/analysis; access to information and expertise; and the nature of deliberation. The key observation emerging from these principles is that many existing participatory methodologies have not sufficiency considered constructivist perspectives on environmental knowledge. It is argued that effective PRA in postnormal environmental risk contexts depends on a number of specific measures being in place that guard against the 'technocracy of participation'. more...