About 3mm long.
No interactions present.
The black line along the hind femur is diagnostic.
Is this bug an aphid mimic? If so, why on earth would it want to look like an aphid?
Hmm... that's a new idea for me. They certainly don't behave like aphids, and I think practically all nymphs of little green jobs look roughly like this, so it's probably coincidence (plus the fact both they and greenfly are trying to blend into the background). And as you say, I really can't see why they'd want to mimc an aphid. :)
Lat/Lng: 51.5, -1.8
OS grid ref: SU1987