Torn between throwing an even bigger strop and curiosity, curiosity won out. Turned out to be not any old moth but a Small Ranunculus! The trap hadn't been on for a few night because of the weather and me being poorly so I can only think it had been attracted to one of the house lights and had found a sheltered spot out of the rain.
So despite the weather we ran the trap last night hoping another might show up but not to be. Although four September Thorn were a bit of a surprise.