Length 2 to 4 mm. This is a difficult genus and examination of male genitalia is needed to separate the 3 species. Criomorphus albomaginatus has a rear genital segment that is approximately triangular in rear view.  The frons (face) has 2 median keels throughout which are white and prominent in C albomarginatus and C williamsi.   The forewings have pale tips.  Both brachypterous and macropterous forms exist.   

There are several similar species; Florodelphax spp. also have white tips to forewings

Can only be verified to species by examination of internal genital structure and external genital segment of males.  Photographs from top down, of underside and of face, showing keels, will support ID

A variety of grassland habitats.

April to August.

Criomorphus albomarginatus is Common; C moestus and C williamsi are both Notable B (ref.: UK Auchenorrhyncha checklist 2021)  

Occasional, but rarely recorded to species

https://www.britishbugs.org.uk/homoptera/Delphacidae/Criomorphus_albomarginatus.html