Solve a disagreement I’m having with my brother in law- nearby plots we’re watching being developed. X is a house already started and I think at wind and watertight. Next plot is down a slope and they have dug out to level the ground which looks like it’s leaving X in a rather precarious position, there’s no more than 6 feet between the already constructed house and the dug out land for the next house, two separate self builds, I am saying the one that has dug out will need to erect a retaining wall, brother in law says it will be the responsibility of X . I can’t see this being the case as he already had the house erected when the other party started to dig. What are your thoughts?