I only know this as my old neighbour was kicking off about the fence between us. She was complaining that it should be replaced as it was falling down. If I didn't do something, she was going to make a formal complaint.
I went to the authority to ask who's fence it was and thats when they told me it's always the left fence when looking to the rear of a property from the front.
My neighbour was complaining because her little rat of a dog was trying to get through the holes in the fence... after a few harsh words from her one day, I went out and took the whole fence down and replaced it with a single strand of wire running the length of the garden and nothing else.
She ment mental and demanded I put a fence up, unknowing to her, there is no law stating you HAVE to put a fence up, as long as there is a dividing line marking a boundary. She then had to control her dog as if she let the dog into her garden it would enter mine and s**t everywhere. This meant her having to take the dog into the garden on a lead everytime

Needless to say, she never spoke to me again. She was a nasty piece of work anyway, lol.