Its definitely Ratty Poo !
I've had the problem in my attic a few times over the last 5 yrs and the guy from the council was quite clear about the little buggers...they can climb up walls,,up internal walls..you name they can do it...check if you got any dropping in the sewer manhole as that's a frequent access route apparently...though how they get out elsewhere is still a bloody mystery.
Strange how they always seem to turn up in winter, it seems the pest control guys thinks its because water tables are up and normal places of residence are washed out so they vacate to warmer climes !!
If you had bats, you'd see the roost marking ( scratches and faeces ) over the dropping zone and that's absent your on a safe bet with Ratty !
best cure...nice big block of rodent poison