A small bug with pale antennae; dark-red/blackish dorsal surface and dark reddish hind femora; found on oak.  Aedeagus of the male has a  toothed lobe on inner margin before apex. 

The Psallus genus includes many small bugs with mottled brown, orange/red or blackish dorsal surfaces. The pronotum and forewings are covered in scale like pale hairs and the tibial spines arise from black spots. Few can be identifed from external characters, and dissection of male to examine the aedeagus (repoductive organ) is almost always needed.  Females are usually impossible to identify with confidence.

Other Psallus, especially wagneri/perrisi on oak and pseudoplatani/assimils on Acer.

Dissection of male genitalia neeed, plus photograph of specimen.  You must note the tree species from which it was collected.

Native oak trees

Local (ref.  British Heteroptera checklist (2021)

rare; possibly under-recorded