The Government do not want to build a third runway at LHR, but they could probably get away with extending the northern runway and getting a new runway built at LGW too. Semantics is the key to this and an extension at LHR is not a new build - I suspect that Zac Goldsmith, Theresa May, Boris Johnson, Philip Hammond et al could just about live with this and it would get Cameron off the hook with BA, HAL and the CBI...
...But not flightpath residents.
They cannot get away with it for one simple reason: that scheme requires permanent mixed mode to be used if the number of movements is to be increased, and if not, there's no point.
That means no alternation and therefore
no half-day respite for anyone under the flightpath, ever.
That alone makes this scheme un-doable. Who knows why it was included in the shortlist.
Utter waste of time when there is already a suitable runway at other London airports that can be used immediately and without having to tear down streets of houses and ruin the lives of those who reside in them.
NHT?
The one distinct advantage of an extended northern runway is this - it provides outstanding political cover for Cameron; he can back it without reneging upon his 'No Third Runway' pledge by spinning it as an upgrade. Zac Goldsmith could probably just about live with it as could Hammond, May and Johnson. Politics is everything. And the fact that it is cheap i.e. £12 billion helps too, especially when rail electrification at £38 billion was seen as too expensive...
If you really think that, please explain why flightpath residents would put up with no respite whatsoever (see above).