Aero Mad,
Do you believe all the passengers travelling thru the London airports originate and terminate in London, in England?
No they don't, many are connecting passengers that, they hope, will not set foot outside the airport ..... however transferring between LHR T1/2/3 and T4/5 has become an inconvenience, National Express do a roaring trade transferring passengers between LHR, LGW, STN, LTN or similar, just how far is this supposed to go?
When I travel with KLM, or Lufthansa, or Swiss etc, I am not required to arrive at RTM and depart from AMS, arrive at DUS and depart from CGN or arrive at ZRH and depart from GVA, one transfers to/from the same airport and this is where London is already failing to compete with the competition.
If Manston were ever to get anywhere the people that would need convincing would be the paying public, people that live in Middlesex only want to fly from LHR, people that live in Sussex only want to fly from LGW, against their wishes they unwillingly need to transfer between the two, try selling them tickets from/to a Battle of Britain airfield on the Kent coast ..... WTF!