I am unsure as to how they came up with £13 Billion! A 12 mile, 4 lane bypass has recently been opened close to me and the cost of this was £52 million. It's lit most of the distance and has been dug approx 40ft lower than the surrounding ground so I cant see how a runway would cost 25 times that amount! I appreciate it would take a lot more abuse from several hundred tonne planes every few minutes, but I would be interested to see how they justify this cost.