A small bug - length 2.5 to 3.5 mm, with a narrow shape. Cymus species have a distinctively punctured head, pronotum, scutellum and forewings. Cymus claviculus has a narrow band without punctures just next to the suture between the clavus and corium.   

other Cymus

Your photographs should clearly show details of forewings and the impunctate band near the corio-claval suture.  This can be difficult to see or photograph in the field, and we recommend that a specimen is examined and photographed.

Dry grasslands and heaths, associated with knotgrass and toad-rush.  

Adult: All year

common (ref.: British Heteroptera checklist 2021 on British Bugs website) 

Occasionally recorded

https://www.britishbugs.org.uk/heteroptera/Lygaeidae/cymus_claviculus.html