How Many Serial Killers Are There In London Right This Instant?

Luther is a very dark but excellent British police show on Netflix; Idris Elba (who infamously played Stringer Bell in The Wire) is a detective with a checkered past that constantly haunts him, and he inhabits what appears to be a gritty version of modern East London, but is actually a parallel universe where every third person is some kind of sociopathic serial killer (it took me a few episodes to get over this absurdity, but it makes the show run at a rapid clip, unlike the world of The Wire, where it could take an entire episode to get a search warrant).