Polymeric nanocomposites were prepared by using cucurbit[7]uril as a 'supramolecular anchor', as well as stabilising ligand to immobilise catalytic transition-metal nanoparticles on the surface of methyl viologen-bearing polymeric colloids. This facile and spontaneous supramolecular approach allows for control over size, morphology and composition of the nanocomposites. The small metallic nanoparticles impart the nanocomposites with great potential in catalysis.