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No privet in immediate area, and it has been busy munching the willow leaves it is on.
I think it must be an Eyed Hawk Moth caterpillar then. No doubt someone with more expertise than me will be along shortly.
foodplant looks like Salix viminalis, Osier, or similar narrow leaved willow
Lat/Lng: 51.5, -2.6
OS grid ref: ST6282