Looking at the contours on my Ordnance Survey map, any new runway would have to be off set by quite a distance to avoid land that drops away quite steeply at the 08 end as it follows the railway line. My guess is that a new runway will be proposed around a mile to the south of the existing runway, which would put it just north of Chiltern Green. It might also not have a 08 / 26 orientation due to the lack of 3000m of relatively flat land following that direction. My guess is that a new runway will point more towards a northeast – southwest direction. By doing this approach and takeoffs will avoid flying over all towns including Luton and Stevenage.
The circle marks a position just south of where I think the runway could be.
http://www.multimap.com/map/browse.c...e=25000&icon=x
Note the spot measurements shown on the map of 151m just south of Diamond End, 146m just north of my circle and the 150m contour line to the west of Chiltern Green. A new airport would then be created in between the two runways.
Remember each contour line represents 10m/ 30ft of rising or falling land which means a new runway will not be placed next to the existing runway as Gatwick did. Land just south of the existing LTN runway peaks at around 160m but drops to 120m at around where a new 3000 m 26L runway would start.