And get this: Not mentioned on the BBC link above, but on another report the agent is quoted as saying "Considering the location, it's really not that expensive."
I don't care if it is opposite Harrods, convenient for Sloane Street, or standing in the grounds of Buckingham Palace for that matter. It's still just an old janitor's closet.
England must operate on some pretty backwards building codes leftover from the 19th century. How does a 10x17' space classify as large enough to be habitable space or a dwelling? A flat for the elephant man...