Seven Dials was an early housing development, built on the west of the City of London in the early 1690s and intended as an upscale residential neighbourhood. It was laid out on a series of streets radiating out from a central point where a sundial with six faces stood in the middle of the road. (The seventh “dial” was the pillar itself.) Unfortunately for the developers, the 18th-century saw the building of the new West End with its fine squares and wide carriage roads. Seven Dials, with its narrow streets, was just not fashionable enough to attract kind of tenants the developers had hoped for. It fell into decay, abandoned to squatters. The once-fine houses were taken over by the lowest class of people who could find nowhere else to live. The area became a slum, known in those days as a "rookery".
Crime was endemic. Donald Shaw, writing of the 1860s, said that: “The walk through the Dials after dark was an act none but a lunatic would have attempted.” There are references (for example in Dickens) two constables venturing in to force some sort of law and order, but I have my doubts. In Disraeli's novel (set around 1840) Sybil is attacked in Seven Dials and it takes a troop of soldiers to save her. In Back Home, when the police to arrive they come in force, provoking a massive riot. I think this is probably a realistic view, at least if you believe Donald Shaw's account: “… the half-dozen constables within view would no more have thought of entering it than they would the cage of a cobra.”