It seems to me that the majority of people on here pedalling the idea of LGW or Northolt being part of a super hub have no idea how transit traffic works?
Whilst it might just be possible to create a secure network between these locations and treat the train/mono rail as airside, it would be very expensive and difficult in practice because you would have non EU pax and domestic trying to move between terminals.
We must not forget that CDG & AMS do all this on site and yes 18R at AMS is a bloody long way from the terminal but it's still on site.
The only sensible solution has be excluded ie R3, Boris island has merit, but it's a twenty year 50bn programe that the UK can't fund right now,R3 meanwhile could be up and running by 2016 without a penny of tax payers money creating a lot of jobs in the current parliament.
How they would deal with the U turn is another matter!