Hacking of plaster from a party wall? For a small patch, probably not, but for a whole wall probably yes. Grand – v – Gill EWCA Civ 554 [2011 ] found that plaster formed a part of the structure and so hacking it away will affect the structure and a party wall agreement may be necessary. In any event avoid removing the render or plaster with percussion or mechanical tools as these are liable to cause damage (typically cracked plaster) on the other side. If there is no party wall agreement then there is a presuming of blame and it is you who will have to prove your work didn’t cause the damage
Taking out a chimney breast? Yes, if its on a party wall?
Taking down and replacing my fence? In most usual circumstances no
Building next to a garage or outbuilding? Yes, basically anything more substantive than a shed, Collier Stevens use a rule of thumb which is if it has foundations it is a structure and the Act will apply.
Excavating for a drain run? Yes, if the excavation is within 3m of next doors foundations and deeper than the bottom of their foundations.
Taking down and replacing the ceiling in my flat? Probably if there is a flat above you