In ever-polarising societies, efforts at land use mediation and agreement between contesting parties are needed more than ever. There is increased scrutiny on roles, responsibilities and representation with pressure to find agreed solutions to social, economic and environmental problems at a range of scales. In this paper, we critically review literatures on policy mediation via the co-construction of knowledge. We then examine a case study from Wales where policy experts were brought together in a hybrid forum to explore ways community assets might be passed on to groups to control them directly. Stakeholders knew at the start of the policy engagement process that they must arrive at a mutually satisfactory outcome. But who steers the solution narrative and how can participants in the process best ensure that the sharing of evidence leads to political traction? Through contemporaneous notes, qualitative interviews, the project’s reports and other documents, we offer intellectual, methodological and policy contributions on mediation and agreement breakdown. We find that some participants from more formal institutional settings are actually unable to ‘leave their expertise at the door’ as recommended. Instead, notions of representation loom large. Some participants with different professional expertises retained a strong desire to control solution narratives. While entirely logical and understandable for these particular stakeholders, arriving at an efficient and equitable solution for all parties was ultimately compromised because of the key issues of roles, responsibilities and representation that we highlight. We conclude with policy implications for contested land use decision-making.