I went out to snip a sprig of rosemary for use in my dinner, when I was distracted by four small but beautiful beetles on the plant. Each one was probably only 7mm long, quite rotund and shiny green with oily bronze stripes and lines of indentations. I hadn't seen anything quite like them before so had to look them up. It turns out they are literally Rosemary beetles, and as the RHS will tell you (via that link) they are an invasive pest that has been sweeping the country over the last few years, working their way out from the South East mainly.
Actually, when I found them they were engaging in spring-time activities as per the photo below.