Background: Debates about evidence-based policy (EBP) were revived in the UK in the 2010s in the context of civil service reform and changing practices of policy making, including institutionalisation of public participation in science policy making. Aims and objectives: This paper aims to explore this revival of interest in EBP in the context of the Government-funded public participation programme Sciencewise, which supports and promotes public dialogues in science policy making. It is based on in-depth ethnographic study of the programme during 2013, considering the impacts on Sciencewise practices and working understandings of engaging in the EBP debate. There is a particular focus on the advantages and disadvantages of categorising public participation as a source of evidence-based policy as opposed to presenting participation as a democratic act which is separate from discussions of EBP. Key conclusions: At different times Sciencewise actors moved between these stances in order to gain credibility and attention for their work, and to situate the outcomes of public participation processes in a broader policy context. In some instances the presentation of outputs from public participation processes as legitimate evidence for policy gave them greater influence and enriched broader discussions about the meaning and practice of open policy. However, it also frequently led to their dismissal on methodological grounds, inhibiting serious engagement with their outputs and challenging internal frameworks for evaluation and learning.