The East India Company, located in Leaden Hall st, held a monopoly on the opium trade starting in 1793. This monopoly required all poppy growers in India to no longer sell to any other competing opium traders. This company played a huge role in furthering British imperialism. Initially, this company was just involved in the spice trade but later became a huge catalyst for the use and access to opium. This company used slave labor as many others did at that time. 

https://www.pbs.org/wgbh/pages/frontline/shows/heroin/etc/history.html

https://www.britannica.com/topic/East-India-Company