Why the plan for Heathrow Hub is bananas

Heathrow wants to expand. Originally this was to be done by building a third or even fourth runway north of, and parallel to, the existing runways. The fourth runway would be fitted in by reducing slightly the horizontal separation between runways. The separation at Heathrow is generous, or very generous compared to Los Angeles or San Francisco.

Now, apparently, Heathrow wants to expand by building one or two runways facing southwest. When LHR was built it had not only the two remaining west facing runways, but also two facing south west (and indeed also two facing north west). These other runways have been consumed by taxiways and terminals, but one southwest facing runway called 23L was in use until fairly recently. Runways are named by their magnetic direction reduced to two significant figures. The L or R suffix is added where there are parallel runways. So rebuilding a south west facing runway would appear to be reasonable.