My Mum's next door neighbour did this today. My folks are away and I happened to drive past just as he was snipping them - mind you he did it with bloody loppers so now the rose is going to be pruned incorrectly IYSWIM. I don't know whether to tell my Mum what I saw or just leave them to it.
I believe you are legally entitled to cut back anything that overhangs, but you are not entitled to keep it. So, fruit, flowers etc still belong to the owner of the plant even if they overhang your property.