Rainbow Greenclock Poecilus versicolor
(In an earlier version of this page I accidentally used the incorrect vernacular name for this species - apologies for any confusion).
The keel on the first 3 segments of the antennae pointed this to genus Poecilus, then a combination of reddish antennal bases, the lack of distinct punctures on the head, the broad flattened area on the sides of the pronotum and the arrangement of depressions on the pronotum all pointed to versicolor, the commonest member of the genus in Norfolk.
Rainbow Greenclock Poecilus versicolor showing basal segments of antenna, frons and pronotum depressions, North Elmham Cathedral Meadows (Norfolk, UK), 19th April 2021
Rainbow Greenclock Poecilus versicolor, North Elmham (Norfolk, UK), 8th May 2020