This project is a non starter, always has been, always will be. Why on earth anyone would try and cram more congestion into LHR wants their head examining in the first place.
As someone else said, we'll be having this discussion in another 7-10 years and by that time, European airports would have built new runways and maybe even new airports and LHR will still be dragging it's heels.
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.