I think you might have hit on something here.

Gatwick has two runways, but only one can be used at any one time:



There is an agreement with West Sussex County Council that there will be no second runway before 2019; but that's not far off now, and assuming that ban is on the operation, rather than the construction, of a runway, there's nothing to stop GIP breaking ground now.

They'd probably need another terminal, though they have built a huge swathe of apron space in the past few years. Almost as if in anticipation of future growth....

My feeling is that after huge resistance to 3rd Runway, the "least worst" option will be a proper second runway at Gatwick as a stopgap measure, coupled with some actions which will make LHR's runways more efficient in the interim, while the long term solution in the Estuary begins groundbreaking, with an opening date of around 2030.