Out of trim:
In my opinion, the Thames Estuary is a Non-Starter anyway!
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.
And the City of London is still at the Western-end of the Estuary!
Hopefully fog is less of a problem with modern Cat IIIB autoland systems. Fogs are only a problem at LHR because the airport is operating at saturation levels, and cannot cope with the extra spacing required for low-vis opps. But with double the inbound capacity, that should not be a problem at Boris Island - the Thames airport.
Birds like open grassland (airfields), as much as they do the sea, so that is a known and manageable problem.
And if the airport is orientated to the southwest (as it should be, into the prevailing winds), the vast majority of take-offs will miss London entirely - including all the suburbs. The quality of life and quality of air will be improved for millions of people (the prevailing SW winds will take any pollution away from London, instead of over it).
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