Who owns the fences are marked on the original block plans of our house.
That's certainly the case with mine.
I thought the council was responsible for the rotting fences running along the side of my house when I moved in, but they refered me to my deeds which showed that the side and rear fences were owned by me.
When I had them replaced for decent quality fencing, I went round to the neighbour separated by the back fence, to let him know I had no objections if he wanted to paint or treat it to his own taste.
I could see over his gate that he was already painting it

I was a bit irritated but just decided to let it go.
I just thought it was a bit presumptuous to go ahead without asking.