Before you be too hasty, have a look to see that there are actually wires going into the top of that burnt-out fuse. From the picture there doesn't seem to be any (unless they're blackened).
I suspect the circuit's been previously transposed and that's why you have so many boxes under your stairs (it seems a bit strange for example that the immersion heater is all on its own).
I suspect the circuit's been previously transposed and that's why you have so many boxes under your stairs (it seems a bit strange for example that the immersion heater is all on its own).
