Published in 1985, it won the Hugo and Nebula awards for best novel, and two years ago it was voted on the NPR (formerly National Public Radio) website as the third greatest sci-fi/fantasy novel of all time, behind only and .

"It's a book that will last forever," says Asa Butterfield, the 16-year-old British star of , who plays the gifted Ender. And there is an undoubted universal quality to a story set on a futuristic earth, 70 years on from an alien invasion. In a plot that feels part , part , Ender is the next great hope, recruited into a military academy designed to forge a new generation of leaders to help combat further attacks.

Financial expectations for are high. This is especially so since, in addition to the book's popularity, the film boasts a hot young cast - from Butterfield to Oscar nominees Abigail Breslin and Hailee Steinfeld - starring alongside popular veterans such as Harrison Ford and Ben Kingsley.

Yet there's also palpable nervousness about due to some unwanted publicity. The source? Author Orson Scott Card, a staunch Mormon, and his public opposition to same-sex relationships and same-sex marriage. Just one example: in his 2004 essay, , he stated: "They steal from me what I treasure most, and gain for themselves nothing at all. They won't be married. They'll just be playing dress-up in their parents' clothes."

In 2009, Card joined the board of the National Organisation for Marriage, which opposes same-sex unions - and his extreme views have been causing waves of unrest. Already this year, when DC Comics hired him to write an instalment for its forthcoming digital-first Superman anthology , there was an outcry from fans and retailers, while Chris Spouse, the artist due to illustrate the project, backed out.

Meanwhile, studio Lionsgate felt sufficiently compelled to issue a statement saying they "obviously do not agree with the personal views of Orson Scott Card". Card was conspicuously absent from the panel at Comic Con, the San Diego showcase seen as crucial for marketing such films to fans. But that hasn't stopped the outrage. One LGBT group, Geeks Out!, proposed a boycott of Hood's film with the campaign "Skip Ender's Game".

In reaction, Card issued a statement to US magazine suggesting that the plot "has nothing to do with political issues that did not exist when the book was written in 1984".

He also added that the gay marriage issue is "moot" following US Supreme Court rulings in June that stated the Defence of Marriage Act discriminated against same-sex couples.

"For all of us, this was an 'Oh Christ!' moment," says Hood, when the issue began to blow up in the media.

The 50-year-old filmmaker didn't learn about Card's views until midway through writing the script. "I faced a genuine dilemma," he says. "I had the moment where I said to my wife, 'I can't believe what he's saying. Should I stop writing the story?' For me, the book and the movie are all about themes of compassion, tolerance and understanding the other. That's the whole premise. So the notion the person who'd written this book would hold the opposite view … I could not wrap my head around it."

Yet he did. The way Hood rationalises it, "art has to stand on its own". He cites the example of Richard Wagner, the 19th-century German composer of the epic . "Wagner was an anti-Semite but his music is brilliant," he says. "Art has to rise above the artist." That said, he is all too aware that Card's views may lose him viewers. "I totally understand anyone's impulse who feels they do not want to see the film because of Orson. I get it."

The controversy may overshadow the film's anti-war message. Particularly pertinent is its depiction of a generation of children weaned on technology. "Even today … my little sister, who is four, can work my mum's iPhone better than she can," says Butterfield.

"I guess in 50 years time, that's going to go to the next level - where children are going to be miles ahead of people of the previous generation, in terms of knowing their way around technology," adds Butterfield. "They've grown up with it, and they've grown up around war games."

It's not such a big step to go from PlayStation fantasy to the reality of drone warfare, with military personnel now trained to drop bombs remotely. Just like Ender, "young people with good reactions on computers are very much sought after", says Hood.

Drafted into the South African army when he was 17, Hood speaks from experience. "Our senses are highly stimulated by action, excitement and the threat of death … but at a certain point when it's real, it's deeply shocking and results in massive psychological scarring. I know both sides," he says. Hood can still remember the aggression that boiled inside him during basic training. "I've been dealing with it ever since."

Whether he and Butterfield will return to the world of Ender remains to be seen. The next book Card wrote was , with Ender in his thirties. The alternative, says Hood, is to write a new story that allows them to continue with their young cast. "Nobody is going to sign off on a sequel until they see how this movie does." And that really depends on how people feel about Orson Scott Card.

opens on November 7