Looks like white cotton wool. A lot of it on what I think is a quince tree.
No identification made yet.
No interactions present.
Looks like woolly apple aphid to me, Eriosoma langinerum: also attacks related species of the Rosaceae, eg Pyracntha, Sorbus, Crategus, cotoneaster as well as apple. It's very common at this time of year, and can be debilitating to young trees. There is a native predatory wasp which parasitizes it, but this is sadly not as common as the pest.
Lat/Lng: 51.5, -1.8
OS grid ref: SU1987