"Alternatively, there is a proposal for Heathrow to have one extra runway to the east and another to the west, or four runways slightly to the west of the airport which would involve tunnelling the M25, filling in a local reservoir and using the existing terminals."

Sounds like it was drawn up on the back of an envelope in the pub. Going to the west, I think the Queen Mother and Wraysbury are rather important pieces of infrastructure, let alone the demolishing of the Colnbrook Industrial Estate and possibly Colnbrook itself. Then there's the the residents of Datchet and Windsor having runways the other side of their garden fences. If you go east, you'd have to demolish Cranford and parts of Hounslow.

Neill