A Runway in the Thames?

It has been claimed, yet again, that, rather than building a 3rd runway at Heathrow, it would be better to create an entirely new airport (a la Hong Kong) on an artificial island in the Thames estuary (http://www.timesonline.co.uk/tol/comment/leading_article/article5489413.ece). The advocates of the scheme maintain that such an airport could operate 24 hours a day (without noise pollution blighting the lives of many people under the flight paths) and that high speed rail links could rapidly transport passengers into London. All this may be true but a Thames-located, 24/7 airport would cause considerable problems for resident bird populations in that area. They could also constitute a hazard for the flights. Birds don't vote but a proper impact assessment is needed before the estuary scheme is floated as a real viable alternative.