Heathrow is a different kind of airport transfer. It is not just the distance, though the journey from Epping is considerably longer than a Stansted run. It is the complexity layered on top of that distance: four active terminals, a drop-off charge system, orbital motorway traffic that can turn a 65-minute journey into a 100-minute one, and a terminal selection error that could cost you 20 minutes of frantic inter-terminal shuttling on a day when you have no minutes to spare.