"That's the lovely thing about movies. They hang around." Joe Cornish on his new film The Kid Who Would Be King

So, are you offended when they do? “Not really. Actually, when you look at early episodes of Grange Hill, they look like Ken Loach movies. They’re all shot on 16 mm. They’re brutal, the school is really cold and ugly, the teachers are shouting at the kids. There’s theft and mugging. Early Grange Hill is really gritty. It feels like contemporary independent cinema. So that Grange Hill I’ll have. I’ll have Todd Carty-era Grange Hill.”

And as for Excalibur. Well, John Boorman’s gorgeous, mad, violent possibly little seen 1981 movie – “I mentioned it on The One Show yesterday,” Cornish admits, “and I got blank looks from Matt and Alex” – was indeed one of the inspirations for Cornish’s film The Kid Who Would Be King.

He saw it back in the eighties before he was a teenager and he has been imagining making a movie about the King Arthur legend ever since.

Indeed, he says, he still has schoolbooks that go back as far 1982 and 1983 in which he has drawn an image of a sword – let’s call it Excalibur – rising out of the bath.

That visual is now one of the central images of The Kid Who Would Be King. It’s a film full of magic, really rather cool flaming skeleton warriors, school bullying, Patrick Stewart, as Merlin, wearing a Led Zepp T-shirt and Rebecca Ferguson dressed in a cloak of vines and bad vibes (she’s the bad girl, Morgana, in the movie).

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Made for, by Hollywood terms, a relatively modest £47million (or thereabouts), the film has a real visual impact. “We’ve made it for half the price of your average blockbuster but everybody worked twice as hard,” its director suggests. “I think it’s got all the scale of a big blockbuster.”

It’s the first film Cornish, who made his name in the mid-1990s with the Adam and Joe Show with his mate Adam Buxton on Channel 4, has made since his directorial debut with 2011’s London alien invasion movie Attack the Block. It’s also, unashamedly, a kid’s film, and that’s an increasing rarity these days.

“It’s definitely a tough sell. Hollywood has become very good at making movies for everybody and most kids’ movies are superhero movies or they’re animation. Most of them are very self-aware and full of meta jokes.

“This is funny and knowing but it’s quite sincere. It’s a movie unashamedly starring kids for kids. Lots of adults say it makes them feel like a kid watching it again.”

The question remains whether there’s a market for such films. “It’s a very competitive market,” he admits. “But the good thing about good movies is they last.

“I had that experience with Attack the Block which did not catch fire at the box office at all, but I’m happy to say that it’s still remembered in a way a lot of movies that did better that year aren’t. That’s the lovely thing about movies. They hang around.”

Commerce versus creativity. It’s the persistent binary in the life of a film-maker. Cornish seems to be falling somewhere in the gap in between. “The opening weekend is a sort of artificiality brutal rat race,” he says at one point. Later, he adds, “It would be lovely to make something that was really commercially successful.”

In the US The Kid Who Would Be King has not been a huge hit, but on pure movie terms it should be said it’s pretty successful. Kids in armour fighting skeletons. What’s not to love?

Must have been a health and safety nightmare though. It’s not like it was when he was a kid, Cornish agrees.

“When we looked for locations to do the big fight in the gym, we found it very hard to find a place with monkey bars because, of course, kids can’t go on monkey bars anymore.”

“I remember people breaking their legs all the time in the playground. There were basically three or four broken arms in the average class in any average week. Not now.”

The Kid Who Would Be King is a movie about kids joining up to take on an existential threat. It talks about togetherness and Britishness and living your life by a moral code. Joe, I say, is this your Brexit movie?

“Umm, I suppose it sort of is. I’m always worried about saying that because it’s not a political movie. But it’s hard not to be, isn’t it?

“It’s a big, fun, goofy action adventure movie, but when you talk about the legend of King Arthur you’re talking about the British creation myth. You’re talking about a legendary king who emerged in a country that was divided, and he unified it.

“It was obviously a relevant myth in the Dark Ages. It felt like a relevant myth when I was 12 because the threat of nuclear war was very present in kids’ psychologies. You’d turn on the TV and you’d see Frankie Goes to Hollywood or When the Wind Blows or something. There was terrorism in central London.

“And today, for better or worse, there are equally divisive things going on. And, weirdly, it does feel like Scotland and Ireland and Wales could separate, which would be terrible, I think.”

There are other views available, Joe, I say. He smiles. “My partner’s Scottish. She was born in Fort William and we talk about this all the time. I can see your point, but unity is a good thing, civility is a good thing, getting on with your neighbours is a good thing.

“I think young children are very moral and they want to know the difference between good and bad. They want to know that adults are a better version of themselves and I’m not sure they’re seeing it at the moment.”

There’s been a seven-year gap between Attack the Block and Cornish’s new film. Some people might ask what the heck he’s been up to in the interim? “And you would be well within your rights,” he says.

“I’d like to make the next one faster but then again, I don’t want to make any old b*******, you know. We’ll see.”

The truth is over the last few years Cornish has been working on projects that in the end didn’t come to anything or are still in development. Most famously, he was working on a script for the original Ant-Man film with Shaun of the Dead director Edgar Wright before Wright walked away from the project.

Wright famously said he couldn’t watch Ant Man when it did come out. Could Cornish? “Yeah. I was there opening night. It was too fascinating for me. I was just so intrigued about how it would end up and I think it’s a fun film.

“I think Edgar’s version would have been very different and I would have loved to have seen it. But that company changed a great deal in the 10 years we worked on that project. When we started, they were looking for auteur directors whose visions would elevate what was seen as quite a trashy genre; the comic book movie.

“By the time the movie came to be produced the industry had changed completely. Superhero movies were dominant. They had found a formula. They’d got confident and into their stride and they didn’t need that level of authorship. Or they needed a different sort of authorship that was more a fusion between their commercial needs and the author’s vision.

“I think Edgar’s a strong enough character to know to step away when that happens. But a lot of the jokes are ours, a lot of the set pieces, the casting, the design. You can still see the movie we wrote in there.”

Cornish is such an affable and open conversationalist I wonder if he’s any different on set. “I don’t think so,” he begins before adding, “You’ve got to be a bit of an A-hole to be a director. I’m kind of learning that. It sort of turns you into a bit of an A-hole.” He pauses. “Umm, I’ve got to figure out why I said that.

“Just because there’s such pressure of time,” he continues. “You’ve got to get it done and you’ve got to get it done well. Sometimes you don’t have time to beat about the bush. You just have to say what you want clearly and then it has to be done really quickly.

“And I always think, ‘God, that’s a recipe to be a bit or an a*******. But my sets are very happy, I think. I’d say to my first Assistant Director, ‘Am I being awful?’ And he’d say, ‘Joe, compared to some of the people I work with you’re a walk in the park.’”

There are other films he wants to make, other projects he’s working on, but the industry is changing so rapidly now. The ground keeps shifting.

Can he ever imagine being a director for hire? “For the right thing … I don’t know. Everything I’ve ever done, I’ve found a way to do it on my own terms. Adam and Joe was a weird, late-night, no-budget thing but it was ours. Some people thought it was rubbish but the people who loved it really loved it because it was unambiguously the product of our personalities. It wasn’t written by committee. It was from the heart, not the wallet.

“But that’s getting tougher and tougher to do. But it’s got to be possible, hadn’t it? It’s got to be possible.”

The Kid Who Would Be King is in cinemas now.