Eventually, Dobkin’s project collapsed and in came Ritchie again, now on a high after his two Sherlock Holmes movies jointly grossed more than US$1 billion. “The stars aligned to make this one happen,” says Ritchie, relieved that his beloved Arthur script has finally escaped development hell. Even then, there were issues with Ritchie recutting the film drastically.

“I’ve seen two versions of it,” admits Charlie Hunnam, who plays Arthur, “and they were very, very different … I would say, less than half of what we shot is on the screen.”

What’s emerged is the movie Ritchie is happiest with: a mix of Arthurian legend, CGI fantasy and some mythological tinkering, with Hunnam’s Arthur raised in a brothel and growing up to be an expert with his fists. Myth-making is hard to do, he estimates. “It’s a very hard genre to pull off, particularly to make it contemporary.” There were other concerns too. “How do you take King Arthur, who is supposed to be a good guy, and make him interesting?”

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Ritchie’s solution was to turn him into a rough diamond. Hunnam admits it was Arthur’s journey, holding the Excalibur sword aloft, that has always interested him. “It’s about self-actualisation, that idea that you have an aspiration for yourself and there’s always going to be challenges and conflicts that need to be overcome to achieve that,” he says.

“What I find really exciting in understanding that is those challenges … the role was internal, not external. You have to conquer your fear within to cultivate the self-belief and confidence to be able to conquer your external challenges. That’s really the basis of Arthur’s story.”

Both Ritchie and Hunnam claim to be hugely inspired by Boorman’s film, which starred Nigel Terry as Arthur and featured Liam Neeson, Helen Mirren and Gabriel Byrne.

“When I first saw it, it was very current for me and I was affected by it,” says Ritchie. Explaining how he grew up sword fighting with his brother, Hunnam concurs: “John Boorman’s Excalibur was one of the top three, if not the, most important films of my childhood. I watched it over and over and over again.”

While they saw eye-to-eye on Boorman, Ritchie is not afraid to admit that Hunnam was not his first choice for Arthur. “I didn’t like him [at first],” he says with a laugh. “But as the process went on, I liked him more and more. And he just won it fair and square on his merit.”

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Hunnam is famed in the US for playing the biker gang leader in the series Sons of Anarchy, but his biggest Hollywood role to date was in 2013 monster movie Pacific Rim. “It wasn’t really [Ritchie’s] cup of tea,” says the actor. “That’s the only thing he’d seen that I’d done. It didn’t show exactly what he was looking for in this role.”

Hunnam – born in England but based in Los Angeles for years – decided to get on a plane, head to London and meet Ritchie. “I wanted him to see me for what I was,” he says.

One of the big problems was his skinny physique. With others reading for Arthur, “about the fourth time Guy brought up how skinny I was, I said, ‘I tell you what, let’s stop all this auditioning bollocks and I’ll fight those other two guys for the role! Put us all in a room together and whoever comes out alive gets the job.’ I think Guy quite liked that!” Fortunately, it didn’t come to that.

At least Ritchie didn’t have any issues with casting Jude Law as Arthur’s nemesis, Vortigern. The British actor, who played Dr Watson for Ritchie in his Holmes films, has rarely, if ever, been the villain. But after playing Shakespeare’s Henry V on stage, Law wanted to explore notions of demonstrating power in Vortigern.

“I liked the idea that he is a guy that is so driven by his obsession with power,” the actor says. “Clearly he’ll do anything for it … He’s like a big fruit gone rotten in the middle and the fruit still smells pungent but inside it’s decay and maggots.”

Law made it clear that he didn’t want any grandstanding speeches, giving them away to the Earl of Mercia (played by Peter Ferdinando). “I think anyone who stands up and screams about how powerful they are, and ‘I’m the best’, usually isn’t. So I quite like the idea of here was a guy who is almost bored, almost absent. He sits and watches the world … it’s like he’s playing a big game.”

The actor even asked the props department to find maps to adorn his tables. “He’s literally moving pieces around a board. To him, he’s the purveyor of all of that,” says Law.

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While Vortigern was, according to some historians, a tyrannical fifth-century king embroiled in the Arthurian legend, Ritchie was not afraid to move the film into the realms of fantasy. “I think some people involved in the making of the film [think] you didn’t need the fantasy aspect. I personally think you did need the fantasy aspect.”

From giant mammoths to squid-human hybrids, it’s a catalogue of creatures that will undoubtedly annoy the purists but please those reared on The Lord of the Rings. Already, the plans are to turn King Arthur into a six-film franchise – an ambitious notion but one that has merit, given the source material.

“There are so many characters,” says Ritchie. “We hardly touch on Merlin, we don’t touch on Guinevere, we don’t really deal with the peripheral knights. So there’s a deep well of stuff there. You can’t stick it all in one [film], because as soon as you do, you trip over yourself.” Leaning across a suitably round table, he smiles. “I’d be very happy to go back in there again.”

King Arthur: Legend of the Sword opens on May 11

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