I originally put this post out under the heading 'HELP". This moth was trapped on St Marys, IOS on 03/10/2013, With a little help from my son, Ben, and birdforum, the answer came within a few hours from Martin Honey and (I think independently) soon after from Dave Grundy - who has also obtained obtained a specimen on St Agnes this October. It is Helcystogramma triannulella - the first British record of this species. Click on the image for more details.