On Black Poplar, caused by an Aphid, Pemphigus vesicarius
No interactions present.
I think this is most likely to be the fourth Pemphigus species which causes galls on black poplar leaves - P. populi. To be certain the causers need to be identifies.
Lat/Lng: 53.2102, -0.555
OS grid ref: SK965691
Poplar hedge to allotments