He is the butterfly ecologist at the Centre for Hydrology and Ecology near Wallingford on the other side of Oxford and, like other scientists, he has not merely studied this issue but conducted impressively painstaking experiments. He has kindly allowed me to quote from an email which I found fascinating - and encouraging:
Meanwhile, I have got one moth to show today - and to ask about - thanks to one of my sisters who lives in London, spotted it on a wall and got this well-focussed picture with the help of one of our nieces. I found myself in the position of many readers of this sadly scale-deficient blog when she asked for an ID: how big was it I wondered?
Using the terminology of those who got the bottom grade in physics-with-chemistry O level, I enquired: "Was it a little scrap or more like a small butterfly/" She replied in similar scientific terms: "Smaller than a small butterfly but bigger than a clothes moth."
From this I deduce that it was one of those nightmares for the ID detective, the pugs, and I'm prepared to make a guess on the basis of a final note from my sister: "To the naked eye, it had a slight green glow which is only partially evident in the pic."
This makes me opt, in spite of the absence of those dots in the official picture of the species, for the dark form of the Green Pug (see example of the normal one a few posts back) which has the rather sinister name of form anthrax. Notorious as the name of a very nasty disease, the word 'anthrax' comes from a Late Latin adaption of the original Greek for 'carbuncle'. It seems a rather mean name for this melanistic (and hence formerly common in London) little insect.