I knew this subject was complicated, but not THIS complicated!
Thanks, chaps, for a most enlightening thread - I'm glad that the right people understand it.
Lucky the current govt has ruled out the 3rd parallel runway, then, otherwise it would get extremely complicated.
For what it's worth, London ATC and 4 airports handle more passengers per annum in aggregate than any other city - NYC comes next (though it handles more movements = more t/props). But note PEK alone has just overtaken LHR.