You are entering the territory of Dickens or Thackeray, Wilkie Collins. If you go to them for information, you will be nothing more than a plagiarist and a thief. Yet you must somehow to put it bluntly invade their territory and repossess it. You need maps, charts. You need spies, agents, correspondents from the past.
Foreign spies are always the best.
They see things the English themselves will never tell you. In the eyes of foreigners one discovers a foreign land, all fresh and new and waiting to be put at the service of a 20th century novel. I live in New York. I went to the New York Public Library which was filled to bursting with the accounts of nineteenth century visitors, not just Americans, but Germans and Russians too. Here the most interesting source was Dickens himself.