By looking at the bios of all these men they are all either engineers, advocates or supporters of the taxation policy that caused the American Revolution. The names listed are in order of their appearance in the work. Charles Townsend was the Chancellor of the Exchequer (The Tax Man Himself). Lord North was Prime Minister of Great Britain from 1770 to 1782. He led Great Britain through most of the American War of Independence. Bishop William Markham was one of the best scholars of his day, and was a staunch advocate of American colonialism. This is an unusual depiction of George III in a casual pose without crown.
This might be interpreted as a portrait of the villains.