@fairflyer
Like the idea of realigning NHT runway and lengthening instead of third Heathrow runway. Probably would cost a quarter or even much less of the £18.6 billion currently estimated for the third LHR runway. A 6 mile tube link between Heathrow and Northolt would be about £1.5 billion perhaps and that would take mere minutes to transit between the two. Add road infrastructure off A40, links to Hillingdon Tube Station, terminal, runway, everything else and that's going to be a couple more billion, tops.
Absolutely crazy not to give that serious thought? Why hasn't it been at the forefront of any of the viable, practical alternatives?