skip1E: I think you and others are too focussed on the market aspect when in reality this decision is more about residents rights to a quiet life, the cost , the environment, the timescale, the destruction of homes and infrastructure and general disruption for years ahead to name just a few angles. we are not france where they have plenty of room to expand. putting another runway at CDG for instance would probably not encounter any of the above problems but to shoehorn one in and outside of lhr is just not sensible on so many levels.
give the industry another runway at lgw and the market will rapidly adjust and make the most of it. airlines and their marketing depts are remarkably good at it. meanwhile lhr can complete its extensive and long overdue overhaul which is already producing 21st century facilities.