Common Footman.
(Eilema lurideola)

It gets its English name from its supposed resemblance to a 'stiff to attention' footman from days gone-by.

Information:
Fore-wing length: 14-17mm. They are very common and distinctive with grey fore-wings which, at rest, are folded round the body. Along the fore-wing there is a thin but pronounced yellow stripe that often reaches the wing tip. The hind wings are not visible because of the folded fore-wings but they are yellow and very obvious in flight. They can be seen flying July-August in most lowland habitats ranging from urban gardens to farmland, wetlands to coastal areas and many woodlands.