Originally Posted by Full Emergency
I think that you might need to re-read my post. The Bye-laws INCLUDE all the Perimeter Roads around LHR. The public roads and parks, you're right, we can not move you on. Inside the LHR boundary we can and normally will.
FE
The roads landside at LHR are covered by the Road Traffic Act.
Each entrance has a No Vehicles sign

with the "Except for Access" rider (whatever that means).
I don't remember any of these being present:

, so you'll have to cite the bylaw which prevents pedestrians from entering the roads.
You will (hopefully) have a better understanding than I of the trespass, obstruction and loitering offences, although I don't see any being applicable.
Loitering = standing or moving slowly
with no apparent purpose. I'm sure you routinely move spotters on and none of them is going to argue the toss, obviously. I am not qualified to comment on whether or not you are legally empowered to do so, but as posted earlier the police can always find
something and no punter will go to the trouble of calling your bluff.