The place would be frequently Fog Bound and Highly Dangerous with the number of Sea Birds that happen to live there; the Bird-strike Risk would be a major concern.
This will rule out any Thames Estuary development. A few years ago, a certain Mr Darling proposed a major new (London) airport at Rugby, my neck of the woods, (prompting a plethora of signs in the area stating "Not now Darling!" It was clearly a red herring as is any proposal to build in/on the Thames. Similar to Rugby, it will be used as a lever to develop one of the existing airports, extra runways, new terminals etc.
Unless of course the powers that be have invented a way of controlling the weather and training the local waterfowl.