Cold, condensation and mould.....

... and/or is your damp proof course (DPC) breeched - there needs to be at least two rows of bricks beneath the DPC and the ground. Do those bricks look a different colour compared to the rest of the house (i.e. if damp they turn darker)? Although sometimes a different harder engineering type of brick is used up to the DPC. Can you clearly see the DPC, I know you said in an earlier post that you believed there is one, they do vary, ours is a slate course and is very obvious except that a previous owner thought it would be a good idea to mortar over them as they must have thought they looked ugly - so I removed that. If it's a modern house it should have a plastic DPC which should be clearly visible sticking out the mortar a few mm's. I'm sure you know all this but worth having a good look at this area outside and comparing it to the rest of the house. The other thing is there an outside rainwater gutter/downpipe that could be leaking? You could also dig down next to the area and bring up the soil, really it should be bone dry next to a house, but if it's soggy it will indicate problems. Fixing should be up to your landlady

 

I will double check the DPC when I am out there later - got to haul down a floodlight and see if I can fix it anyway. I will get a photo of the fungi too @Zigs, just to confirm, as Googling orange peel fungus brings up images of something that is orange - the one I have is more like old/dried and darkened orange peel (more of a light browny-orange if that makes sense)