I got 3 snaps of this chap on the trail camera. At first I assumed it was a fox but then I noticed the little stump for a tail and the white rump. The next thought is domestic dog and that seems the most likely to me, in fact it is probably all it can possibly be, but it is pitch dark on a night with no moon and about 3 miles from the nearest access, there were no people nor other animals on the camera around this time. In fact I doubt if there have been any people in this area since I dropped the camera off nearly a month ago as the ground is very soft and the only prints I could see were my own.
I've tried to crop the photos so you get as big an image as possible though this does leave the night time shots of the mystery animal a bit grainy.
First a shot of a very poor sika calf in a similar location, just to give an idea of size. As you can see the bad weather has hit the deer hard, though it is shedding its coat as well which makes it look even worse:
Now a shot of a fox in pretty much the same position as the mystery animal. The fox does have 4 legs, it is just that the rear two are lined up and so it looks like only one. In this shot the fox, which I think is a pretty big fox, is in about the same position as the mystery animal:
Now the three shots of the mystery animal cropped so you should get pretty much 100%, though I tried to leave the same grass/rushes in shot as with the fox image just for scale. I'd say it is a bit bigger than the fox. Note the short stumpy tail sticking up in one of the photos and the white rump. Also the ears seem a lot smaller than I'd expect with a fox.