Gatwick/Heathrow
Pprune buddies have hit it right on; if you think of Heathrow as effectively "two airfields" it does not handle double Gatwick movements by a big margin.
I back the Boris plan.......look at Hong Kong!!!! You need the one thing Heathrow can never have...SPACE. Compare the size of the Heathrow site to Paris CDG or Amsterdam....its like a football field by comparison.
Get away from the draconian operating restrictions that strangle Heathrow growth.....build another bigger airport.....unleash ATC and show how much traffic can be shifted.