Every diamond has its flaws, and even a borough as posh as Westminster had a neighbourhood overflowing with crime and debauchery. Tothill Fields, or Devil's Acre, as Charles Dickens called it, was so bad that cops were afraid to walk through it. It was so bad that it helped popularize the word "slum" in the 1850s.
It is believed that the area became so rundown because it was used by the monks of Westminster Abbey to house criminals and debtors seeking sanctuary. Another possible reason is that the land was a marshy hotbed for diseases, undesirable to the wealthy people of Westminster. Whatever the reason, Devil's Acre was a blot on the city that many wanted removed.
Because of its proximity to Westminster Abbey, Parliament, and so on, Devil's Acre was seen as a cause to work for by London's philanthropists - not like Whitechapel, which was far away and nobody had to look at it. Dickens wrote extensively about Devil's Acre as a young reporter and in 1847 he worked with the millionaire Angela Burdett-Coutts to found a safe house for Devil's Acre prostitutes called Urania Cottage. Missionaries worked the area constantly in the hopes that religion would somehow make them not poor. The philanthropist Adeline Cooper, with help from Lord Shaftesbury, bought a pub in Devil's Acre and converted it into a school for the orphans who populated the area.
For all this effort, it was the establishment of London's sewer system that contributed most to the gentrification of Devil's Acre. The sewer system helped drain the marshy water from the neighbourhood, which suddenly made the land desirable to real estate developers. Victoria Street was created to cut through Devil's Acre, and residents were displaced into newly-built social housing.