Dear Jason,
 
Neil is of course right to turn to Lemmon v Webb to try to find the answer.  But I'm not sure that the case provides direct authority for his claim that "since a landowner has a right not to have their land interfered with by tree branches, they are entitled to exercise the right even if it kills the tree, if there is no other way".  That said, I think that this conclusion can conceivably be reached if one reasons by analogy.
 
According to summary of the case on Westlaw, R v Rosewell (1698) 2 Salk 459 says this:
 

If H. builds a house so near mine that it stops my lights, or shoots the water upon my house, or is in any other way a nusance to me, I may enter upon the owner's soil and pull it down; and for this reason only a small fine was set upon the defendant in an indictment for a riot in pulling down some part of a house, it being a nusance to his lights, and the right found for him in an action for stopping his lights.

 
I think, then, that one could argue by analogy that an affected party should similarly be entiteld to trim overhanging branches that cause a nuisance, even if so doing is destructive of the tree.
 
Best,
 
John Murphy

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