I always thought this was about Jimi Hendrix - he and Jagger were
both living in the Chelsea area of London at the time. Another
verse has a reference to the demonstration - Jagger made at least
one appearance at the Grosvenor Square demos outside the American
Embassy.
So the song is about London and life in London at the time - Drugs
and politics and the rest. I'm afraid I don't think the twin
cities come into it.