Length 2.5 to 4 mm.  Brachypterous (short-winged) and macropterous (long-winged) form occur.  A brown planthopper, with a broad pale zone down the central part of the pronotum and scutellum.  Females cannot be identifed with certainty; males can be separated by examination of internal genitalia. 

other Muellerianella

males

Males can be identified by microscopic examination of genitalia.  Photographs of a specimen from top down will support ID

Damp grasslands/ditches etc. with Tufted Hair-grass (Deschampsia cespitosa).

Summer-Autumn.

Common (ref.: UK Auchenorrhyncha checklist 2021)

Few records, possibly under-recorded due to ID difficulty

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