Leiodes litura
Although litura is by no means the commonest Leiodes this individual keyed to litura using both the Hackston and Duff keys. For all but the clearest couplets I checked both ways just in case I'd made a mistake but every other path ended up with a dead-end. I also checked it carefully against the desriptions of each of the "three commonest species" given in the Hackston key in order to make triply sure I'd eliminated those. I dissected it in order to confirm the ID by genitalia and found bits of what at the time I thought had been the aedeagus, but nothing comparable to the diagrams in Duff - and concluded that I'd messed it up. Subsequently I have dissected another Leiodes, a female, and realise that the bits I thought were part of the aedeagus were in fact its ovipositor, so not a male after all. In any case it was no help so the ID is based on external characters alone. It's length was 2.3mm and was swept from White Dead-nettle.
female Leiodes litura, St Mary's churchyard, North Elmham (Norfolk, UK), 8th June 2021