Swallow-tailed Moth ( Ourapteryx sambucaria )

Another insect showing signs of having had a hard life.

I have never seen a Swallow-tailed Moth before and the swallow tails aren't very visible on this somewhat decrepit specimen.  Having looked it up I am told they are fairly common throughout UK apart from the very north.  So how come I have never seen one?  It appears they are strictly nocturnal and unless they settle for the day somewhere you are going to come across them you are unlikely to see them.  This one chose to settle on the door, we had been in and out a number of times before we noticed it.