Asaphidion curtum
This very attractive beetle turned up in my moth trap. At the time I must have felt confident that the ID was clear from the photos I took (all of which are below) as I didn't keep the specimen or any additional notes. Looking back at it now this feels a little careless as this is not generally an easy genus to identify and it's not a particularly common species. Anyway, having reviewed both the Hackston and Duff keys and checked photos online, I think I got it right (though always welcome views of others with more experience). I was in possession of Duff at the time and would likely have checked Hackston online too, and in the absence of any notes to the contrary I am confident that the size would have been within the stated range for curtum. In fact I think pretty much all the other characters given in the key are visible in the photos other than the aedeagus which I don't appear to have examined (maybe it was a female?). Reassuringly the close-up of the pronotom shows a distinct angle at the side bristle, which seems to be one of the clearer pointers to curtum rather than flavipes.
Asaphidion curtum, North Elmham (Norfolk, UK), 4th May 2021