A small planthopper associated with Marsh Foxtail, Alopecurus geniculatus.  It is often brachypterous but macropters also accur.  The body is mostly dark brown or black, and the wings are brownish or yellowish.

Other Javesella species

male

Dissection of the male is needed to confirm identification.  Also photograph the specimen, and note habitat and associated plant species

Damp grassalnds, edges of water bodoes, etc, on Marsh Foxtail and other grasses

Common (ref.: UK Auchenorrhyncha checklist 2021 on British Bugs website

rarely recorded