In the opening post he wrote that the outhouse is a spur from the ring but that it feeds a double socket and then a spur for the light. So it is a spur from a spur.
Junction box feeding outhouse - it has one double socket with a fused spur off it for a light.
It's fused. Loads of garages/outbuildings/sheds have a spur coming from the house and then a FCU for a light.