Decided that even wasting £20 on this is pointless, and giving that the wildlife cam may have problems detecting such a small animal, problem no doubt amplified with a cheap one and getting bored of trawling through all the chinese garbage on ebay I've gone for a £7 IR illuminator and my dashcam, I'll build/modify a little box for it all to sit in to keep it dry and see what shows up.
A less technical solution has solved it, went out to the garage a couple of nights ago to find a couple of rats chowing down on the dropped seed from the bird feeders.