Ben: Hmm... I recall there being a glass-walled room on the terrace on top of T2
, there were toilets there and a small cafe. Has it all been shut down? On a Sunday you could find anything upto 50 regular spotters with cameras, radios etc. etc. spending time there. Perhaps other BAA managed airports do not have this but LHR T2
definitely did and to my knowledge still does. You can of course choose to go and try various car parks and other corners around LHR
, but get anywhere near the fence and one of the police cars that patrol the perimeter road will shoo you away.
As for perks, I guess you are right, nothing there except they may not interrogate you so much if you do end up prowling around roads and spots where others normally don't go to and the BAA police find you.