Back on thread I just had a thought. If they leave AF1 at Stansted (coz his nibs is off into Europe on visits quite quickly) they may well leave it in the VIP area. Driving into Stansted from the M11 you will see signs to the left for an industrial estate. Follow that road into the estate and you end up right by the fence to the VIP parking area. Should be able to get some great pix from there.
PS. I know this because this is where I get my flight meds when I'm in the UK. The last time I was there the UAE 'Royal Yacht' was parked there.