About 8-10mm long. Strong greenish tinges in places. Devouring leaves of a young silver birch.
No interactions present.
I would say it was P.pomaceus.
It's not P. pomaceus as it lacks femoral teeth, and P. pomaceus is confined to nettles as a food plant.
For info on P. pomaceus, including explanation of femoral teeth, see:
Lat/Lng: 51.5, -1.8
OS grid ref: SU1987