In my workshop I had a rat, there were loads of droppings and after resorting to poison, I'm pretty sure he is no more. However, in the course of my investigations, which included setting up a camera, I discovered that a mouse was taking the rat bait and not triggering the spring traps.
Since this started, I bought 2 rat traps (in addition to the Nooski I already had) and two mouse traps. Both mouse traps have disappeared, including the one that was on camera (which takes 3 photos, it's there in 2 of them!). One of the rat traps has had bait taken from it but the other one, a Victory plastic model, which has a bit of chocolate as bait, is taking a mouse a day. I think I'm up to about 7 now...
Thing is, there's no obvious food source in there but it seems I wasn't dealing with a lone individual. I'm sure it's not the same mouse feigning death because there are a number of tiny corpses in the spot where I dump them, in the hope that something will clean them up...