Prior to 9-11 it was fairly common practice to use a ladder to get above the high fences
at Londons Airports for Aircraft portrait photos,
even Heathrow as illustrated with M.Kahl here in 1997 near the petrol station
for taxiing shots to 09R runway, but I very much doubt you would be left in peace nowdays,
and this position possibility has disappeared anyway now, due to triple anti-spotter fences!!!!