I assume that's what it is.The building is about 4ft. square,thatched,one door,facing camera,in the southwest corner of a large garden.No-one was available to ask.It had gated access from both field and the road.
It aint a shed Ian, Its an earth closet. An outside toilet. A hole in the ground, with a plank of wood across, obviously with a hole in the plank as well. As the hole slowly fills you sprinkle earth on the contents. When the hole is filled, you dig a new one, shift the shack above it, and start all over again.