In　many　application　problems　such　as　the　electromagnetics,　the　unknowns　are　usually　defined　at　the　edges　to　satisfy　the　continuity　requirement.　This　paper　develops　the　first　positivity-preserving　edge-centred　finite　volume　scheme　for　diffusion　problems　on　general　unstructured　polygonal　meshes.　The　edge-centred　unknowns　are　primary　and　have　associated　finite　volume　equations.　The　cell-vertex　and　cell-centred　unknowns　are　treated　as　auxiliary　ones　and　are　interpolated　by　the　primary　unknowns,　making　the　final　scheme　purely　edge-centred.　The　scheme　has　a　fixed　stencil　due　to　the　fixed　decomposition　of　the　co-normal,　which　makes　the　scheme　very　easy　to　implement.　The　positivity-preserving　property　is　rigorously　proved.　Numerical　experiments　indicate　that　the　scheme　has　second-order　accuracy　and　positivity　for　heterogeneous　and　anisotropic　problems　on　highly　distorted　meshes.　©　The　Author(s)　under　exclusive　licence　to　Sociedade　Brasileira　de　Matemática　Aplicada　e　Computacional　2024.