Guv,
Greenham Common? get real!, no sensible transport to cover the south east market, having to drive past LHR to get there, and a further 30 miles at that! By the time Greenham Common was being talked about, T5 was well on the way. Why drive past LHR to get to Greenham? With LHR operating normally how would you propose the integration of Air Traffic would work? Think you might get a few slot delays as an absolute minimum!. In your virtual world it might work, but not in the real one. As for a marine airport why bother? theres less environmental impact in upgrading STN to meet the forseen requirement.