Continuity mistake: At the battle of Edgehill when Crowell's cavalry and Prince Rupert's cavalry are in the middle of a melee and you can see a wound on Crowell's left arm, the same wound he receives at Naseby. It is clear that the scene was meant to be used for the battle of Naseby but was cut and used at Edgehill.
Continuity mistake: Peers and commoners (like Cromwell) are seen sitting in the same chamber in Parliament. In reality, of course, the Houses of Commons and Lords are separate chambers.
Continuity mistake: Cromwell purges an altar of "idolatrous" objects by knocking down candlesticks. He begins by knocking down the second from the left. In the close-up, the candlestick is standing again and he has to knock it down a second time. This happens twice in the same scene.