In what way is London used as a setting in the novel, Blood on the River?

The first few chapters of the novel, Blood on the River, take place in London, where Samuel has been in the poorhouse, on the streets, and finally in an orphanage. Samuel is cared for by the operator of the orphanage, Reverend Hunt, who takes Samuel and Richard from the orphanage to James Town colony. London is the seat of English government and power, and where all the James Town settlers embark from. It is dirty, full of people and full of dangers for those who fall afoul of its laws.