Where is 21 Grimmauld Place?

[Steve]

Is there anyone here who is from London or is familiar with London,
who might want to speculate on possible REAL London neighborhoods what
could be potential locations for #12 Grimmauld Place?

Neighborhood that at one time were nice well kept middle class
neighborhood, that have not endured the test of time very well, and
are now run down. 

It would have to be on the East side, which makes sense because I'm
lead to believe that the East End is a working class low rent
district. Am I correct in assuming that the 'East End' is an very old
London neighborhood? Remember they flew east, and told Harry if he got
separated he should continue to fly east, and the re-enforcements
would join him.

One odd fact that makes it almost impossible for Grimmauld Place to be
a real neighborhood is how long it took to fly there doesn't seem
consistent with it being a 20 minute walk to King's Cross Station,
which unless I'm mistaken is roughly in the Charring Cross Road
neighborhood. Flying time seems to imply a far east neighborhood, but
a 20 minute walk seems to imply a central London neighborhood.

I know it all fiction, but I'm curious.

bboy_mn