Most properties in Medway appear to be afflicted with some form of damp.
If you rule out an obvious cause of direct ingress, which may include: a missing roof tile, a leaking pipe; or there is a build up of black mould and lack of ventilation appears the most reasonable option then, what is it about Medway properties specifically that causes the majority to have some degree of damp?
A broadly encompassing answer is the nature of the local geology and the materials and methods that were used during construction and how these two factors affect the properties today.
Although scaled down to accommodate the dimensions of adjoined terrace properties, the Rochester end-of-terrace pictured above features a highly ornate flank-wall facade which imitates or perhaps exceeds the aesthetically pleasing characteristics of the more up-market local villa style properties of the same era.