I would like to hear a lot more facts about this one.
I know LHR very well, and each of the four potential holds for a 744 are a serious run from any part of the fence - probably 09L is the shortest, but I could be wrong. Even at 09L the sprint would be 2-300 metres. At 27L you would need to be of Olympic class to get from the fence to the a/c in time to climb aboard. All of the other holding a/c crews would have a view of what was going on and could call the tower.
If this report is correct the cameras suggest a journalistic stunt, but one that is too stupid even for a new editor wanting to make a name for herself, or himself, or whatever.