is this mouse or rat dropping? (or even bats) as its hard and does not turn to fine dust.
Without some measurements of the length of the stools I cannot be sure, but they look like brown rat droppings. Mice droppings are about the size of uncooked Basmati rice grains and rat droppings can be considerably longer (12-15 mm) and much thicker.
I originally went for mice, but looking up in the attic this looks like a lot of urine!! There so much movement going on in the gable its like a rave up there
We had rats in our attic/ground floor ceilings last winter. Our neighbours' landlord got some cowboy builders out to replace the external door posts/door to their gas meter room (under their stairs) and they left large gaps at the bottom of the door posts where they met the concrete doorstep. Rats were getting in through those holes and then were climbing up inside the cavity wall into their ceilings and attic and then through the partition wall into our semi-detached house. I had to find the problem and fix it because their landlord insisted it was their fault as they must be leaving the back door open! (He made no attempt to find the problem and ignored their complaints.)
They make a lot of noise overnight as they are nocturnal and they will eventually chew on your electrical wires and possibly through plastic pipes, which can have serious consequences for you and require costly repairs. I lived in a student house with a rat infestation many years ago and they chewed through wires causing an electrical circuit to trip out.
In that house the rats got into the attic by a different route, which could be how they are getting into your attic if there are no holes in your external walls (or those of adjoining properties). They will be coming up from the sewer. Have you taken up the nearest manhole cover for your drains? If you do, you may find that the rats have been tunneling out of your house's sewage pipe/sewer intersection alongside your sewage pipe and have got access to one of the rainwater drainpipes on your house that come down from the roof. They can then climb up the drainpipe, come out on your guttering and then squeeze in between the roof tiles and the eaves and climb up into your attic. That's how they did it in that student house I lived in.
If that's how they're getting in, all you need to do to stop them is to cut some 30 cm square pieces of fine chicken wire (<10 mm mesh) and roll them up so they are over half the internal diameter of the roof drainpipes, then bend them halfway down 360 degrees so they are shaped like a wedge. Insert the wedge shaped end into the top of your rainwater drainpipe where it meets the guttering and push it down until it is firmly stuck in there. That will allow rainwater to go down the pipe but will stop rats from getting out of the top of it. That's how we stopped the rats getting into my last student house (where I was a tenant). You will also need to mend where they are tunneling out of the sewer, but that might be impossible if you don't have access. The long-term guaranteed fix is to insert a one-way steel rat-flap in the sewer pipe between your house's sewage pipe output manhole area and the public sewer.
