The Reddish Light Arches (Apamea sublustris) is a moth in the Noctuidae family.
This species, which is found locally in the South of Britain, is similar to the Light Arches (Apamea lithoxylaea) This species has a slightly darker and broader forewing though, and has a length of 18-21mm.
This species flies from June-July.
Reddish Light Arches ~ http://www.flickr.com/photos/qwertyqwertyqwerty/