As a house mover of some experience, these boundary walls area slightly grey area, I have copies of my house deeds (available to download for a few pounds) but to my left is a boundary which is difficult to fathom. As my house is on a hill, there is a 12 metre drop into next doors garden, with a supporting wall, on top is a 2 metre fence, which I have always maintained. A problem with the massive supporting wall would be expensive and cause a big upheaval to both properties, but who is responsible is certainly not clear on the deeds. Anyway it will soon be somebody elses problem cos I' moving!