The scene where William Wilberforce sings "Amazing Grace" at the card house was actually directly sung from Ioan Gruffudd at that moment. In the last several takes, a playback was used, but it is Ioan singing. Director Michael Apted had no idea whether or not Gruffudd could actually sing. Little did he know, Ioan is an accomplished soloist and choir singer. With a little practice, Ioan performed for the first time on set while the cameras were rolling. All much to the surprise of the cast, crew and director.
A special screening of the film was shown in Buncrana, Co. Donegal in Ireland. This was in celebration of John Newton's link with the county, when in 1748 his slave ship, the Greyhound, came ashore after surviving a terrible storm. This event began the spiritual journey for Newton, which culminated in his authorship of the song, Amazing Grace.
During the conversation between Thomas Clarkson and William Wilberforce it is questioned how a person can remain loyal to a king who shakes hands with an oak tree and see Germany through his telescope. The quote, spoken by Clarkson, is a reference to King George III who, by the contemporary belief of history and scientific research, was known to have suffered from porphyria which was possibly provoked by his use of arsenic.
William Wilberforce's family line lives on today, and most recently, their name was in the news in the United Kingdom after Susan Wilberforce (the Baroness de Stempel), a direct descendant of William, stood trial for the murder of her first husband in 1989. She was eventually found not guilty, and the murder remains unsolved.