Jan 31, 2012
221B Baker Street is the apartment of Sir Arthur Conan Doyle's famous fictional detective, Sherlock Holmes.
Tom is right, Doyle made up 221B. Baker Street was not extended until years later. There was actually a big squabble between the Abbey National Building Society (located at 219-229 Baker Street from 1930s onward) and the Sherlock Holmes Museum (set up in 1990, located at 237-241 Baker Street, but with a plaque reading 221B) over which building was the real 221B.
In the comic, Rupert Swope drops Tom Taylor off in front of 186 Baker Street, a few blocks away. I was able to find the exact spot on the street where Tom is dropped off, right in front of the HSBC bank and the Box Office for City Tours.