Occasionally I'm woken in the night by a whimpering-wailing sort of sound that eventually dies away. I rather assumed it was a sound of animal pain and alarm, and therefore that perhaps one of our local foxes was earning its keep by catching a rat. It certainly wasn't the screaming bark of their mating call (the kind they use in TV dramas to signal that it's creepy at night in the countryside and Something Nasty is about to happen).
But one night I looked out to see a fox chasing another, and as they passed under my window it was clearly the chasing fox that was making the noise as it saw off an intruder. So it's presumably some sort of territorial warning, the vulpine equivalent of "Git orf moi land!": or - this being the East End - "Gerrahta my rubbish bin!"