severe environmental impact on the area. Plus there are other airports round London that could be more easily developed. The problem is getting people from one airport to another (though I think there are plans for a fast train between LHR and LGW) so they feel everything has to go through one hub.
it will be gold for the owners. The airlines aren't so impressed, as they suspect they'll end up paying for it (before they pass the cost on to passengers).
Years spangle and of course it will in real terms (not just paper shuffling look how we have manipulated the figures) go over budget by at least 25% if not 50%
Will the future need it though. Tech will allow you to 'be somewhere' from your own office. Jet pollution is likely to become a green issue. And besides, why should everyone have to go to Heathrow to fly somewhere ? It's busy enough already and many would prefer somewhere more local.
Harmondsworth has a wonderful medieval great barn; I don't know what will become of that. Sipson is already being used to house asylum-seekrs, as far as I know, so they'll have to go elsewhere too.