Mystery visitor

I went up to the allotment, mooched about a bit, dug a few old things up, sowed a few nasturtium seeds....was just about to leave when I spotted something small and shiny on the rosemary bush. Turned out there were two of them, erm, at it. And then I noticed a third, on an adjacent twig. Just watching, or waiting its turn perhaps?

Anyway, can't find them in our insect book. Any thoughts, blippers? (The size of a ladybird, or thereabouts.)