Autumn flutter

I'm not sure just what this is (comments please?) - but it has left it a bit late to be out in the Autumn sun on pal Colin's boat-launching tractor (hence the rust). After a sailing season of gales and much rain, it has been a remission to get a few late weeks of sunshine as this butterfly (moth?) is demonstrating.

Stop Press:
Thanks to comment-poster BillG for this identification. It is a Comma