Some years ago the Met did a drugs bust (sorry, executed an MDA warrant)on a house, solely because of the high infra red signature from the roof. Excess heat emissions are often indicative of a cannabis grow, as the heat lamps etc give off a lot of, er, heat.
Anyway, there was no cannabis to be found, but they discovered 2 things. The house belonged to a PCSO, and he had no loft insulation. And that, children, is why you're supposed to get some corroboration from other sources before going to a magistrate.