The point of this is that if you decide to demolish your rear extension at some point in the future then they will be in a bit of a tricky position as their nice new extension will suddenly be al fresco.
It's extraordinary unlikely they will want to use his wall to build off. Obviously check the plans. They wouldn't be able to easily tie it into the extension for a starter.
Chrisbmx how much did that lunatic next to you cost you in party wall fees and how fucked off were you?
The point of this is that if you decide to demolish your rear extension at some point in the future then they will be in a bit of a tricky position as their nice new extension will suddenly be al fresco.