London, the Metropolitan Police, founded by Sir Robert Peel in 1829, was headquartered in a district known as Scotland Yard. Scotland Yard was originally a geographical term, denoting an area of Whitehall that contained many government buildings. These buildings included the official residence of the surveyor of works to the crown, which was occupied by Inigo Jones, and later by Sir Christopher Wren. John Milton lived in Scotland Yard when he was working for Oliver Cromwell from 1649 to 1651, and it is apparently from this association that a slang reference for police, two hundred years later, was 'miltonian.''
"When Sir Robert Peel located the new Metropolitan Police in
Whitehall, the correct address for the headquarters was No. 4 Whitehall Place, but the police station there had an entrance from Scotland Yard proper, and the press always referred to the police as Scotland Yard, until the term became synonymous with the force itself.'
"Scotland Yard grew rapidly in its early years; in 1829 the total force was 1,000, but a decade later it was 3,350, and by 1850 it was more than 6,000, and would increase to 10,000 by 1870. The task of the Yard was extraordinary: it was called upon to police crime in an area of nearly seven hundred square miles, containing a population of two and a half million people.'
"From the beginning, the Yard adopted a posture of deference and modesty in its manner of solving crimes; the official explanations always mentioned lucky breaks of one sort or another – an anonymous informant, a jealous mistress, a surprise encounter – to a degree that was hard to believe. In fact, the Yard employed informers and plainclothesmen, and these agents were the subject of heated debate for the now familiar reason that many in the public feared that an agent might easily provoke a crime and then arrest the participants. Entrapment was a hot political issue of the day, and the Yard was at pains to defend itself."
(pp. 166-7, 'The Great Train Robbery' by Michael Crichton - Landmark)