Grayling - Hipparchia semele
seen here, scrunched up in typical habitat & pose, it's hard to believe Graylings are the largest of the UK's Browns, weighing, or rather measuring, in at slightly larger than Meadow Browns & Marbled Whites (the latter being, rather confusingly, also a brown)
see adjacent image for a photo of a Grayling with eyespots on forewing showing