I agree with Skipness's comments. The only thing likely to cause more outrage in West London than building a third runway (apart possibly from unlimited mixed mode operation) is closing LHR. Looks like you are stuck with a two runway Heathrow. With the new East terminal this could handle 90m pax p.a with an average of just under 200 per atm which is achievable by replacing 319s with 321s & 772s with 773s - nothing drastic really.
If the number of transfer pax remains constant that would equate to a 50% increase in terminal pax which may be 20 years growth. Its not exatly the long term planning you see in France or the Middle East, but it I suspect that we can muddle through for a while yet.
Obviously UK aviation will suffer from loosing transfer traffic - unless someone can develop MAN as a credible hub (perhaps, as suggested on the Virgin thread, it could be VS). Its interesting that the proportion of seating on KLM long haul devoted to premium is just over half that of BA so perhaps the lower business traffic base could be overcome. It would require a high proportion of premium traffic to be transfer though as O&D premium traffic outside London is low. AMS, FRA & ZRH all have environmental constraints whilst CDG is not user friendly. MUC & Berlin are ones to watch. If everywhere is environmentally constrained a "green field" transfer hub combined with more Air Transat style infrequent operations which includes secondary airports may be the way ahead.
The trouble is airline business models are based on high frequency. Championing the free market approach but constraining capacity don't go together.
As a frequent leisure traveller I worry about business traffic squeezing on leisure seats hence an increase in costs but as long as business traffic is peaked airlines will upsize to meet the peak in demand so it may not be a big an issue as I fear.
Current aviation policy - muddling through. Future aviation policy - muddling through. Don't say we don't have the experience of how to get through.