Many houses in London suffer from damp, one cause of which is "raised ground level" - where higher soil bridges the damp course (if present) and prevents evapor

Many houses in London suffer from damp, one cause of which is "raised ground level" - where higher soil bridges the damp course (if present) and prevents evaporation from the wall base. Why did the ground level get raised? Because inhabitants were collecting horse manure to fertilise their gardens, for several decades after the houses were built. (The cure is to replace it with gravel next to the wall)