Mereley because it's the police who repeat an Urban Myth (and even if it's on television)doesn't make it true.
As a caravanner, one myth I regularly hear is the one about stopping overnight on a French motorway service area, and the occupants are gassed and robbed (usually by Gypsies or similar). Specific circumstances are NEVER referred to. Camping and Caravanning Club magazine run a column by a Detective Constable who was happy to repeat the story without attribution. My suspicion has always been that this one was put about by French Campsite owners who don't like the idea of caravanners stopping overnight for free!
There's quite enough real stuff to worry about in life without circulating this sort of rubbish.