We appreciate all the good wishes, support and ideas on how to dispose of a neighbours body if necessary. We certainly have some good and creative friends around us . . .

He didn't go that far, but I knew someone who was so annoyed with his neighbour that he jumped the fence in the dead of night and, uh, "adjusted" the markers for the foundations of a new building that seemed sited mainly as an FU to him (and was approximately three floors tall before he objected to loss of light - it was one level before they got permission, but that was still taller than the wall beyond it).
I've not looked for a few years and I can't see it on Streetview because they've planted hedges in front of the twisted walls, but as far as I know, there is still a building with an interesting discontinuity where they cut a layer of bricks about ankle-height to get the building back on the level and it's slightly smaller than originally planned. I wonder how much that cost. Presumably it was cheaper than demolishing and starting over, but can't have been by much...
I still don't really understand the beggar-thy-neighbour attitude, but maybe that's because I only really remember having one problem neighbour over the years and our current ones seem especially lovely.
Good luck!