Picture the scene: you glance out of your kitchen window to see your neighbour making his way towards his shed. He opens the door, turns on a light and instantly a rudimentary laboratory is revealed. On a table, a jumble of wires, powders and liquids lie in anticipation and even from this distance, the ominous icon of a biohazard symbol shimmers in the fluorescent light. He returns into view, clutching a timer; its display casts a green pall across his features.
Should you call the police?