A small metallic moth, an Eriocrania sp, probably Eriocrania subpurpurella (Lepidoptera: Eriocraniidae). This was one of several that were flying around some bushes in a clearing near an oak tree (oak being the host plant for the larvae of E. subpurpurella).
I took two specimens home with me. One had lots of purple dots on its wings (this must be the fastuosella form mentioned and illustrated here):
And the other had only one or two purple spots (this is the common form):
First photo and specimens taken in Whiteknights Park, Reading, UK, on 2014-04-06.