My wife and are are avid spotters and I'm a past Heathrow employee.
Back in the 60s there were at least two commentators on the Roof Gardens, based in a well-equipped box overlooking the apron on the airside of the Queen's Building. Between commentaries they played popular music over the PA syste - hence my love of Glenn Miller and Mantovani!!! I got to know Stan Little and Flo Kingdon through telephoning them for registration numbers when I saw anything interesting arrive. Stan (little by name, little by build) was an avid spotter who introduced me to Air Britain. Flo' was not a spotter but always willing to help. Stan passed on many years ago but Flo' is still alive and well, although long since retired from working at Heathrow.
"Spectators" who erect ladders are surely asking for trouble. My wife and I have spent many hours standing close to the 27R threshold, spotting and photographing aircraft with no problems at all. We park our car on a convenient grassy patch and police and BAA security vehicles have passed us in their dozens with no hint of any objection to what we were doing. Guess they view two old codgers as no-risk.