Heathrow are happy to have hordes of BBC personnel crawling everywhere, encouraging our interest in all things aviation, yet try and follow up that newly fostered interest the next weekend by taking little Junior down to look at the airplanes/aeroplanes/aircraft/planes, and you're more likely to learn about the working methods of P.C. Plod than those of your local friendly international airport.
Actually the Police at LHR are some of the more switched on in the UK. Just don't try parking anywhere you shouldn't and you'll be fine. Spotting from the Central Area car parks is a no no mainly because of the amount of sat navs getting nicked, anyone loitering makes them nervous. (Based jobsworth PCSOs only seem to work office hours, just saying they're invisible at weekends too.) The real Police have seen me up against the fence with a Nikon more times than I can recall and not so much as batted an eyelid.