At several points in the movie we see handshakes, notably Wilburforce with other MPs. Handshaking was popularized 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).
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.
A Member of Parliament says "bloody" on the floor of the House of Commons. At the time, the word was quite obscene; this never would have happened, and if it had, it would have resulted in the disgrace of the member.
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.
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.
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.
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.