Dot Moth.
(Melanchra persicariae)

The most obvious feature on this dark moth is the white kidney-shaped mark on each wing.

Information:
Whilst this can be confused with a dark version of the Lesser Common Rustic moth the slightly larger size and glossy, almost black, blackground colouration alongwith the two white kidney marks indicate that this is a Dot Moth.
Fore-wing length: 16-21mm. They fly June-August over many gardens with flowers as well as open or wooded areas.