Thiol-functionalised multiwalled carbon nanotubes (MWNTs, average outside diameter ∼10 nm) assemble into thin films on a liquid–liquid interface. Combined with citrate-stabilised gold nanoparticles (NPs, average diameter ∼10 nm) MWNTs form uniform, extended quasi-2D nanotube-nanoparticle heterostructures which, being on average only a few tens of nm thick, are self-supporting on the microscale and can span macroscopic surface areas up to 10 cm². MWNTs in these heterostructures are interwoven and interlinked with nanoparticles. The nanotube : nanoparticle ratio in the film can be conveniently controlled by the ratio of components in the liquid phase. The electrical resistance of MWNT-NP composites varies only slightly with the percentage of nanoparticles incorporated in the film, indicating that the electrical properties of these structures are mostly defined by nanotubes. The effect of the presence of nanoparticles on the resistance of MWNT-NP films is highly dependent on the scale of the measurements (electrode geometry) and is qualitatively different for the sub-50 μm regime as compared to the macroscopic regime.