One of the easiest ways to get onto the apron at LHR (if you really wanted to) would be to set off the fire alarm. You are then directed, not escorted, from the BA exec lounge down onto the apron at T1 under the bellies of the boeings/airbuses. OK they let you take your gin with you, but it always amuses me (and it happens with regular monotony) that not only do you now have access to the A/C, but you you are also mustering under a big tank of aviation fuel in a fire evacuation. Odd really.