Closure for a container comprising a cover (3) attached to a skirt (4) by a line of weakness so that the skirt remains on the container after opening. The skirt is retained on the container, to prevent removal and refilling with counterfoil material, by an annulus (10) (preferably a shape memory alloy) which has been shrunk onto the skirt, preferably forcing it into a waisted region of the container. The annulus is preferably stronger than the container so that it can be removed only by breaking the container.