Much discussion has been 'aired' on these over the years and slightly worn ones in spring following hibernation can present a challenge! The hind edge of the forewing looks reasonably straight and the apex is almost square. Small but quite distinct whitish spots are present along the costa. If anybody thinks it is 'just a Chestnut' I am sure you can let us know! It looked 'different' to the 10 or so Chestnuts seen in the nearby wood the night before.