Factual error: In the scene where the king attempts to seize the five members from Parliament, Cromwell makes a dramatic refusal to leave and proposes various "Laws" to prevent his arrest. Cromwell was not one of the five members whom the King tried to arrest and no law can come into force until it had been signed by the reigning Monarch anyway.
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.
Trivia: After the execution of Charles I / Alec Guiness, Oliver Cromwell / Richard Harris returns to his home. Sitting by the fire, he is consoled by his wife: he can now put the cares and worries of war and politics behind him, and enjoy a quiet life as a country gentleman. This cosy domesticity is rudely interrupted when some of his old colleagues arrive to tell him tell him that he is now needed to run the country. He protests that, as a country gentleman he would be unfit for such a role, but he reluctantly assumes power. In fact, by the time of Charles I's execution Oliver Cromwell was one of the most powerful political figures and military commanders in Britain, and actively continued commanding armies in Ireland, Scotland and England, and involving himself in government. Although rejecting a suggestion that he should be crowned king (after much deliberation), he was quite willing to take the title of 'Lord Protector' and govern England, Scotland, Ireland and Wales until his death in 1658.Rob Halliday
Oliver Cromwell: O Lord, Thou knowest how busy I must be this day. If I forget Thee, do not Thou forget me.
King Charles: Mr. Cromwell, you are impertient.
Oliver Cromwell: Such issues are beyond good manners, sir. Catholicism is more than a relgion. It ia a political power. Therefore, I am led to believe there will be no peace in Ireland until the Catholic Church is crushed.