Confidence: It's likely to be this, but I can't be certain.
Notes: The presence of a short diagonal dash at the tip of the forewing may point to this being Ruddy as opposed to May Highflyer. The final example of variation in the species given on page 214 of Waring, Townsend and Lewington shows a similar tan/ochre (perhaps ruddy) colouration and gives the multi-banded pattern on the inner forewing. I can't conclusively rule out the highly variable July Highflyer but H. ruberata appears to be a likely candidate? The grey outer crossline also seems to fit. I havent personally seen the species before.