A third runway at LHR will no doubt help ease the situation in the medium term, but where's the room to expand and grow after that?
In 15-20 years time, will LHR be creaking at the seams again? Is there room for Terminal 6? 7? 8? Is there room for r/w 4? 5? Probably not, unless a large chunk of the surrounding built up area is utilised.
Surely it is time for a new airport to be built, away from built up areas, with purpose built roads and train links, and with plenty of land on option for future development and growth.
Will this happen? Probably not.