What airport proposal(s) has London seen after WWII?
There was one more proposal before Thames Estuary Airport. That was the Cublington airport, which was rejected by planner Colin Buchanan,as "an environmental disaster." Later the government rejected the proposal of this airport, and rather went for Thames Estuary.

Other than that, there are no more proposals for new airports, but there are certain plans for expanding existing Heathrow and Gatwick. 

The Airports Commission says there is a need for one additional runway in the South East of England by 2030.
It has shortlisted three options:


A third runway at Heathrow
Lengthening an existing runway at Heathrow
A second runway at Gatwick


Read in detail about all of them HERE