Ridley Scott has shared that he used a special technique to decide the length of the cinema cut of his new film Napoleon.

The 85-year-old director will have a three-and-a-half-hour version of the film that comes to Apple TV+ later this year, but the cinema cut will be around an hour shorter.

Scott is known for his lengthy epics, including Gladiator and Kingdom of Heaven, and discussed how he uses a certain factor to retain some tightness in his films.

Speaking to Sky News Scott shared: "I have something that's called the bum ache factor - you're sitting there going, 'Oh God, there's another hour!' You got to be really sure that you're running a three-and-a-half-hour movie that's actually worthwhile, people get weary.

The Argus: Joaquin Phoenix plays Napoleon in Ridley Scott's filmJoaquin Phoenix plays Napoleon in Ridley Scott's film (Image: Ian West/PA Wire)

"When I'm cutting… you're constantly watching out for 'Where are we bending and why is it bending?' Is it because I'm tired or is it because this story's just going on too long?"

He added that "longer can be a disaster," calling it "a natural fault" most directors "wrestle with".

Ridley Scott fires back on historical accuracy criticisms for Napoleon

Criticism has been aimed at Napoleon due to its historical inaccuracies with the trailer showing cannons being fired on the pyramids in Egypt as one example and lead actor Joaquin Phoenix using an American accent.

In response, Scott said: "If he talked in an Italian accent, people would have criticised me. And if he talked in a French accent, they would have criticised the French. So, it's best to just go back to what [Joaquin] was.

"If you're engaged by him, be engaged by him. And I think and I'm fully engaged by anything Joaquin does so I never even question it… I don't think it matters."

Reaction to the film in France has not been favourable but this is not something Scott was surprised by.

He shared: "I had a major premiere in France with a big room of a lot of important people. Their reaction was very, very, very enthusiastic. So, they're going to look for anything that can find fault, but they always do, I'm used to it."

Napoleon is out in cinemas from today (Wednesday, November 22).