The Serpent is the best BBC drama series in ages — god knows how it slipped through the net — but I still think it most unlikely that I shall stick it through to the final episode. It’s not the style that’s wrong but the subject matter: do we really want to spend eight hours of life in the company of a smug, ruthless serial killer who murders at least 12 people — and more or less gets away with it?

Up to a point The Serpenthas addressed this problem by trying to make the central figure not the killer, Charles...