You should call Lewisham Planning urgently , and email, ccc the Mayors/CEO's office, probably enforcement but the case officer would also be good, and tell them that the owner appears to be commencing development in advance of planning permission being obtained also a tree has been cut down, and let them decide whether action is appropriate. If they don't know whats going on they can't do anything about it. Its not just cheek, its illegal, but the developers are probably relying on no one noticing. I do recall a developer in Islington bulldozing a building which was about to be listed over one weekend. It got on the news. I don;t think our rather bland legal system can do much about it post event.