penance wrote:
If the tree is overhanging the boundary, the neighbour is legally
entitled to have every overhanging part cut back to the boundary line.
Even if the overhanging section is the main leader of the trunk.


Not so, it is reasonable as long as the work carried out does not pose
a threat to the tree, this is assuming the tree is healthy and not a
threat to property or people.
There has been a precedence set in court for this (in the UK). I have
the reference in my college notes somewhere.

What is reasonable? There is no question of reasonableness in this at
all. Any part of the tree overhanging their property is a trespass.
The neighbour can cut it off (although the branch/trunk/whatever
remains the property of the original owner)..