Actually, London used to have one area code, "01".
Then at some point it was split into inner & outer, and there was endless one-up-manship about whether you had an inner or outer London code. (obviously, inner London was posher)
Then at some point it was split into inner & outer, and there was endless one-up-manship about whether you had an inner or outer London code. (obviously, inner London was posher)
But it seems odd for London, when there are plenty of posh areas in outer London, and run-down areas of inner London. Maybe it was more for businesses to appear 'central'?