Do I need consent from other owners to put a dummy CCTV camera in the common close on my perimeter wall? UK?

The owner of the flat above us has put undesirable tenants in the property who are constantly displaying anti social behavior with loud music etc, when we asked them to turn it down he had an aggressive rant on our doorstep, we have since had problems with their visitors peering into our property and the close is not secure as the door is broken and there are lights out, to feel safe my fiance put up a dummy camera but now the owner of the flat has asked us to take it down, where do we stand on this?