Muggers don’t carry umbrellas. Murderers don’t carry briefcases. Kidnappers don’t carry Tesco bags. These are the sorts of utterly illogical things I have been known to tell myself on a ten-minute walk home from the Tube station in the dark (past well-lit houses, on familiar roads, in a ‘nice’ part of London) as I try to stop my heart pounding quite so violently when someone happens to be following me down an otherwise empty street.