Ingrailed Clay.
(Diarsia mendica)

Nestling in an egg box in the moth trap.

Information:
This was very difficult to pin-down and was a toss-up between Ingrailed Clay & Small Square-spot - on balance it was the Ingrailed Clay that got my vote.
Fore-wing length: 13-17mm. They fly June-July in open woodlands, gardens and scrub-free areas such as heaths and moorlands.