Iron Prominent.
(Notodonta dromedarius)

Resting on a stone wall.

Information:
With a fore-wing Length: 18-24mm, this is about an inch or so long. It has a very memorable dark brown to grey fore-wing with reddish brown streaks towards the head and a cross-band of the same colour in the wider part of the wing. They can be seen flying from May-September near to rivers, heaths, broadleaved woodland and scrubland and, sometimes, luckily for me also in gardens !
The are resident and fairly common over most of Britain.