Last year (or maybe th eyear before) the local council held a 'consultation' and sent a leaflet round with 3 options on it, 2 of which were for a new runway south of the present runway, re-routing the A23 by varying degrees, and the 3rd was for 2 new runways, the southern one and one to the north of the north terminal.
I think the latter was to scare the local branch of the Nimby brigade...