I hear all kinds of strange wildlife noises at night because the back of my building backs onto part of the Horniman Gardens. I have heard some truly horrific screeches, one of which repeated for about half an hour, sounding not unlike a small child screaming, but louder and animal-like. I'm guessing it was foxes as I've seen one several times - last time running down Manor Mount with a Sainsburys ready meal in its mouth.