Revealing mistakes: Near the end of the movie, Clarkson is sitting at the grave site of Equiano. While he's talking, the blowing wind causes the cardboard or foam headstone to move.
Anachronisms: The Duke of Clarence uses "nobless oblige" as his reason for saluting Wilberforce's achievement. However, the first recorded use of the phrase was in Honoré de Balzac's book "Le Lys dans la vallée", written in 1835 and published in 1836. Wilberforce's last appearance in Parliament was in 1824, when he resigned due to illness.
Factual errors: Charles Stuart Fox was never "Lord Charles Fox". He was in the House of Commons until he died.
Factual errors: Charles Stuart Fox died 13th September 1806 and so could never have made his comments about William Wilberforce after the abolition of the slave trade. (Slavery had been abolished in England in 1772.)
Errors made by characters (possibly deliberate errors by the filmmakers): There were at least 3 grammar mistakes: several uses of "I" when "me" should have been used. Wilburforce also says "By who?" As a graduate of Cambridge, he would have said, "By whom?"
Anachronisms: The tune to which the song, Amazing Grace was sung was not used until some fifty years later.
Factual errors: The House of Commons sat in the St Stephens chamber of the Palace of Westminster at the time. It is a long, narrow room, not the debating chamber shown in the film
Anachronisms: Wilberforce's reference to "millions of years" doesn't fit. Even non-Christians of that period would not have thought in those terms.
Anachronisms: During the boat trip to see the slave ship, servants are shown pouring from the distinctive bottle of Dom Perignon champagne. However, the brand was not introduced until 1936.
Anachronisms: Early in the film a Papillon or Butterfly dog is seen in Brooks. While Papillons were very popular in the late C18th, the erect-eared Papillon shown is thought to date only from Victorian times. The drop-eared Phalene or Moth Papillon would have been a more usual choice for the movie.
Factual errors: The movie originally portrays Banastre Tarleton, the Liverpool MP, participating in a Commons debate in 1782. Tarleton did not enter the House of Commons until 1784, and could not have debated on negotiations with Americans as he was not yet an MP and was in fact, on parole from his disastrous performance in Virginia.
Factual errors: After the French Revolution, Charles Fox did not side with William Pitt the Younger. Whilst they were both members of the Whig Party, Fox was a prominent member of a pro-revolutionary faction of the Party, as opposed to Pitt's anti-revolutionary stance. This difference in opinion would typically pit them on opposite sides of the dispatch box.
Continuity: William Pitt's deathbed scene: when Pitt says "I'm scared", a blob of pale yellow discharge can be seen beneath his left eye. The shot then cuts to Wilberforce, but as soon as it cuts back to Pitt (after about a second) we can see that the blob has vanished.
Anachronisms: Towards the beginning of the film, Barbara Spooner refers to Napoleon as the ruler of France. This scene takes place in 1797, two years before Napoleon came to power.
Anachronisms: At several points in the movie we see handshakes, notably Wilburforce with other MPs. Handshaking was invented by John Adams in America to replace bowing, which Adams considered submissive and not fitting a government of the people. Handshaking did not arrive as an accepted form of greeting in Great Britain until much later (some say the 1850s).
Audio/visual unsynchronized: During the hymn Amazing Grace sung at the wedding, Barbara is seen singing "but now am free" but is heard singing "but now I see".