I've been checking these poplars near Hampton for several seasons without any luck but knew they must be there as the trees are riddled with holes to the point where several have fallen over. Struck lucky this morning with two scampering up one trunk. I think it was a male and female, the one photographed being the male with more pectinate antennae and a bushy rear end. See here for some excellent, instructive pictures of a pair 'in action'.
This adds another square to the VC31 map for this species.
Hornet Moth Sesia apiformis, male
The result of years of work by some moth larvae!