if they are surrounded by urban sprawl.
There's a fair amount of room around LHR. In fact the problem is the flight path over influential rich people and marginal constituencies. Much better to demolish a load of villages with new railways rather than one half-empty village in a pretty drab part of West London. NOT!
This makes no sense, has no strategic planning, will kill domestic access to Heathrow and put the next government in the position of having to solve the problem which will only get worse.