The moth is like a grey version of the Small Fan-footed Wave, which does call here, and also easily mistakable for one of that infuriatingly hard-to-ID tribe, the Pug Moths. The Moth Bible warns of this risk and I can bear it out, having puzzled over several pages of Pug illustrations in a vain attempt to track it down. The clue to its real identity, for me at least, lies in the black dots in its hindwings. Lots of Pugs have a dot on the forewings, but none go in for one on the hind ones.
'Small and dusty'. incidentally, is a good description of the grandchildren after a lovely time yesterday at the fake beach in the Olympic Park, above, which is wonderfully well-used.