Dark Arches Moth.
(Apamea monoglypha)

At first sight a blur of brownish patterns ...

Information:
They can vary from a mid-brown to an almost black colour but if you can see a pale "W" towards the centre of the outer edge and a large oval and equally large kidney mark and the general shape as for the moth in the photo then you are looking at a Dark Arches moth.
Fore-wing length: 19-26mm. They fly June-August and can be seen just about everywhere in Britain. They are often attracted to light & can also be seen on flowers where they will rest, quivering and with wings outstretched.