michael adams laid this down on his screen :
Isn't this risking unwarrented distress, never mind cruellty to any adult
birds and
nestlings who may find tjhemselves trapped in a nestbox which has plummeted
to ground as a result of a rope failing "prematurely"

Might a suitable legal notice above the entrance to the nesting box,
'Use at your own risk' - obviate the risk of being sueded by an injured
bird?