Phyllobius is a genus of weevils. As far as I could tell, this one is Phyllobius argentatus, and it was on hazel, at the top of a
NS3878 : Path through the woods, and not far from the foot of
NS3878 : The Hundred Steps.
(The following notes are intended mainly for entomologists who might wonder what the identification was based on; that is why I have not explained the terminology, though I usually would: as the picture shows, the green metallic scales also cover the underside, and the setae are semi-erect; also, though it is not evident from this angle, both antennal insertions are clearly visible from above, and the pale femora are toothed.)