Agonum marginatum
This is an 8.5-10.5mm long bright metallic green beetle with yellow edges to the elytra, in the family Carabidae (Ground beetles) and one of eight UK species in the genus.
Widespread and locally common, it's usually found on muddy and marshy edges of ponds lakes and streams and being an efficient flier is quick to colonise suitable habitat.
There are similar-looking green ground beetles, in particular Chlaenius vestitus. Agonum marginatum has more rounded hind margins of the pronotum and an upper surface which is both smoother and less hairy.
''Agonum marginatum'' is a species of ground beetle in the Platyninae subfamily. It was described by Carl Linnaeus in 1758 and is found throughout Europe, North Africa, Siberia, West Asia, as well as on islands such as Canary, Azores, and Madeira.