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Answer = Three.

1: "City of London". Also known as "The City", "The Square Mile" [not very "square"]. Basically the site of the Roman settlement.

2: "City of Westminster". Originally a separate settlement, grew greatly once a Royal Palace was built (that was destroyed but reason why the Houses of Parliament are also known as the Palace of Westminster).

3: "London" = the area defined by the GLC (Greater London Council).

Oh ! And don't get involved in Counties [past and present] Police, Local Government or postal addresses - everything is odd, as it should be.

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