Identification of Eupteryx species can be difficult and requires careful examination of markings on vertex, pronotum and forewings.  The arrangements of spot on the vertex and face distinguish this species from other very similar leafhoppers.  It is usually found on water mint. 

Eupteryx melissae and E decemnotata

detailed photographs are needed, showing patterns of spots on face and vertex, and pronotum

wet grasslands and marsh, with water-mint

Local in southern Britain (ref. British Bugs website https://www.britishbugs.org.uk/homoptera/Cicadellidae/Eupteryx_thoulessi.html

Rarely recorded

https://www.britishbugs.org.uk/homoptera/Cicadellidae/Eupteryx_thoulessi.html