We present the novel use of Photocatalytically Initiated Electroless Deposition (PIED) for the deposition of metal films with highly ordered arrays of sub-μm (hemi)spherical pores directly onto the surface of insulating organic membrane-based substrates. This is achieved by sensitisation of the target substrate with a TiO2 photocatalyst followed by the self-assembly of a hexagonally close packed polystyrene microsphere template at the substrate surface. Metallisation then occurs through PIED into the template interstices and directly onto the TiO2 sensitised membrane surface. The dimensions of the resultant pores in the deposited metal are determined by the size of the template microspheres while metal film thickness may be controlled by the deposition period. The fabrication of nanoporous metal by this novel method adds a conductive and permeable metallic structure of high surface area to an otherwise electrically insulating polymer membrane surface. Such metallised insulating membranes have potentially wide applications in membrane and separation technology, desalination and electrode / solid electrolyte composites for fuel cells.