Crumbs - where and when and do you have any hindwing pics. That's a mega special moth to catch in S Wales.
Sorry to disagree, I think this is a Large Yellow Underwing.
My first thought was Large YU too, but Clive is a very competent moth'er so I expect he has his reasons for the ID. I asked about the hindwing in hope of clarification/elucidation.
Saw this on Facebook. I'm afraid I'm with Steve, that this is just Large Yellow Underwing.