Lime hawk moth
It's definitely a moth. This is all that I could say for sure. I can see a bit of green....possibly....if I squint a bit. Moths pretty much all look the same to me. Except that some are big and some are small.
A colleague at work told me that this was on the wall outside our building. He is quite accomplished at identifying moths and butterflies. He assures me that this is a lime hawk moth (Mimas tiliae).