Scotland Yard, London Metropolitan Police:

Also known as Scotland Yard, the Metropolitan Police serve greater London (with the exception of the original square mile, served by the City of London Police). It was founded in 1829 by Sir Robert Peel, whence the nicknames bobbies and peelers. It’s headquarters, Scotland Yard, is so named for its location where the kings of Scotland resided while in London, although the headquarters have moved three times, with both the second and third locations being called “New Scotland Yard.” To my knowledge, its jurisdiction does not extend beyond the metropolitan area, although in Holmes’ time, local police would gladly request the help of Scotland Yard.