A small (5-7mm), very slender straw-coloured bug with short 2nd antennal segment.  The 1st antennal segment club is brown and paler than the dark clubbed 4th segment.  The ends of the hind femora are also dark.  The tip of the wing membrane is rounded and marked with black.  

other Berytinus species

close up photographs showing the identifying features.

Often associated with medicks on calcareous soils.

All year.

Adults overwinter, mating early in the spring; the new generation is complete from July onwards.

Common  (ref.: UK checklist 2021 on Britiah Bugs website)

rarely recorded

https://www.britishbugs.org.uk/heteroptera/Berytidae/Berytinus_montivagus.html