The common marriage custom of 19th century England that is reflected in this passage is the tradition of seeking the father's approval or consent before proposing marriage to his daughter. In 19th century England, it was considered important for a suitor to obtain the father's permission before proposing to his daughter. This tradition reflected the patriarchal society of the time, where the father or male head of household had significant authority over his family's affairs, including the marriage of his daughters. In the passage, Mr. Darcy meets with Elizabeth's father alone, indicating that he is seeking his consent or approval before proposing to Elizabeth. This reflects the importance of this custom in 19th century England and the role of fathers in arranging marriages for their daughters.