It is also cobblers to suggest that a 3rd runway at LHR will be entirely funded by the private sector - nope. The public sector will be paying more than a chunky wedge in terms of servicing the airport - transport costs for one.
And the project is not shovel ready either. It will be bogged down in the courts for at least 2 years and the environmental case will have to be watertight to the nth degree or it will be bye bye.
Personally I don't see the need for another runway, but then I am almost certainly in a minority.
If the Tories want one (and the Labour Party as well) - run on that platform in 2015.