Investigating droppings on front doorstep. Conclusion of investigation, which involved a microscope, is that they are Brown Long-eared Bat droppings. This means they are still living above the door lintel under the porch roof. I'm glad about this because a few years ago when we had someone rebuilt the porch because its supports were rotting, he discovered a couple of bats roosting inside one of the rotting beams when he had already taken half of it away. He built them a house and attached it to the wall. When they emerged from hibernation, they went looking for their old 'house' and ended up in DD's bedroom. All very exciting. Anyway, it's good to see they are back in their old place but with good wood around them 
Must let the local bat man know.