inOban -
The fact remains -as has often been stated - that City is the only real London airport - although Heathrow is in an outer London borough ( but with a Middlesex address). Obviously - Stansted, Luton, Gatwick and Southend are in reality nowhere near London - but as this has been done to death I will shut up now. BUT I would say that I understand that Charing Cross has always been regarded as the official "centre" of London.
PS. Nice to see passengers awaiting their flights relaxing on the grass outside the SEN Terminal this afternoon - not sure you can do that at STN!!