Rail link the airports
Last time the govt said they would build somewhere new, it was on Maplin Sands I think. Quietly during all the political posturing, they were building three lanes of M11 up to Stansted and two beyond to Cambridge. Then guess what? The airport that was developed was Stansted. This time they talk about Cliffe, and all the time a new terminal (I think) and junction improvments are being carried out at STN. It will be STN not Cliffe.
Secondly, there is spare capacity it STN and a bit at LGW. Given that there are not going to be longhaul services out of regional airports in a big way due to lack of demand, we are going to have to go to hub airports. Why not make all three London airports effectively one, but putting a triangular HIGH SPEED rail link between them, which is seamless to the pax (no need to pick up bags etc) and only takes 1/2 and hour and runs regularly (and is free). At the moment getting the bus from LGW to LHR is a real bind and takes ages, if I could do it in 30 mins it is just like a normal transfer and no longer a problem. It would then solve the BA type problems of two hubs and duplication of service. LHR could then become all longhaul and STN and LGW could become all shothaul, with the advantages of airports more tailored to aircraft size.
I think that the government are not brave enough to do this, and another runway or two would be needed to cater for growth and a 'safety bolthole'. Underground tunnels are expensive - but then so are some of the other solutions in other countries such as Kansai.
I used to live in London but now live up north and would be happy to take a regional flight to LGW and transfer to LHR if only it wasn't the pain in the bum it is now.