A lot of people are being confused by the term segregated mode, not too surprising as in the original description there was some ambiguity. By studying subsequent references the ambiguity resolves to the following.

The red arrow signifies the wind direction, of course it will rarely be exactly lined up like this but aircraft can fortunately tolerate quite a lot of cross wind.

When the wind swings right round everything changes ends because landing and taking off is always done into the wind. Its airspeed over the wings that generates lift. On take off wind speed adds to ground speed to give greater airspeed hence better lift. On landing wind speed maintains lift, to touch down with minimum ground speed.

Now it is very easy to see how BAA can say that Takeley etc will not be overflown, It also moves the noise of departing aircraft twice as far away from Elsenham than is currently the case. If you remember your schoolwork, sound diminishes by the square of distance so it wont halve it will go down to a quarter.

This now possibly explains some of the reduced land grab because if you think about what is happening on the ground, the runways are offset. A landing aircraft runs off the end of its runway with a short taxi to the terminal then another short taxi to the nearest end of the taking off runway. When the wind changes the traffic on the taxiway reverses direction too. All the alternatives involve taxiing to or from the distant end of the runway and aircraft on the ground are very inefficient.