Confidence: I'm as sure as I can be.
Notes: I follow the advice on the HantsMoths website to separate these two. There they use the yellow marking on the dorsum (or back edge) of the wing. In P.purpuralis this is large and - particularly - has an even convex edge on the side nearest the base of the wing. In P.aurata this is either absent or - as in yours - broken into fragments. I'm sure many of my early records of P.purpuralis were this species. Almost all garden records are.