Originally Posted by
Asturias56
I think they were laid out that way due to space considerations - with the two main roads (at the time) to the west out of London where they are they'd have had to juggle things quite a bit to fit in NE-SW runways of any length
That's my understanding, too.
Pretty well from the start, the two E-W runways were longer than the other 4 (5) and were the only pair that it was relatively easy to extend further (in a westerly direction) in stages because of the open countryside in that direction.