Gonzo, I understand your argument about the people who work at LHR, the businesses who have based themselves close to LHR etc. However, I am sure that employees would prefer to work at a facility that is easier to work with, is possibly easier to access (which in itself is clearly something that would have to be part of the plan for the new airport), and perhaps even mean an improvement in general living standards.
Fair enough, Thames Gateway is close to Essex and Kent, relatively expensive and very densely populated, but the whole Crossrail proposal included extensions to the east and west, connecting Slough, Reading and Maidenhead to the Crossrail system, and extending eastwards too. Thames Gateway now has connections to the continent via Eurostar, which could quite possibly be included in the proposal and the plans (similar to SNCF and AF working together with the Thalis/TGV station at CDG).
I don't think the corporates would consider this the end of the world either. If a switch is done seamlessly (in the order of Hong Kong etc) they would have plenty of time to either buy or lease new real estate if they really wanted to.
Sadly, NIMBY syndrome, whichever way you slice it, will be the end of LHR or indeed ANY transport extensions/improvements in the London area. You can be guaranteed that Sussex, Hampshire, Bedfordshire and Berkshire would NOT want a mega airport anywhere near them. Essex is already moaning at STN, and Kent... well, the complaints about moving Eurostar from Ashford to Ebbsfleet were enough to make my ears bleed.
In short - we're buggered.
S.