MV, You are correct that the airport was allowed to expand the terminal by up to 15% of the original floorspace without planning permission. They have used this quota with the check-in extension and the extra baggage reclaim area. The airport must show that the walkway is an operational structure, built on operational land and does not increase capacity. An operational structure is exactly what it says, it aids one of the basic functions of the airport of getting passengers from point A to point B. The terminal is not an operational structure because it contains many other areas, retail for example, superfluous to the airport's primary aim of getting passengers and baggage from drop-off to the plane. The current walkway was constructed as an operational structure. In order to achieve the aim of construction without planning it will have to be a simple walkway with nothing inside it. The plan is to have holding areas at each stand at ground level. The passengers would walk out of the terminal on the mezzanine level from the new walkway between Burger King and the rest of the terminal. They would continue to the stand when they would drop down via stairs and lift to ground level. At this point there will be a holding area. The whole building will not be able to have seating, save for a handful for disabled passengers, it cannot have any immigration control, no retail outlets (even vending machines). It will be a transit shed getting passengers from A to B without the need for a bus. Passengers will be called forward to their departure gate only when the plane is ready for boarding and not before. They will not be able to go to the gate to wait as one does at Heathrow. The walkway will simply remove the queues from between the seats in the main departure lounge. There cannot be seating areas in the holding areas because this will increase capacity. One suspects there will be a series of movable barriers such as is found in the immigration hall to control the flow of passengers in the holding area as they queue to board. If the design is more comprehensive than a very basic walkway with holding areas where passengers stand it will need planning because it will fall outside the scope of Permitted Development. I agree that this is going to be the opening skirmish of a long planning road.