'I don't want to get into a fight with the Royal Society,' says Tom Harper – clearly about to do just that – 'but they were the first people to say, "Why didn't you pick a female scientist?"' The British director behind Wild Rose is talking about his new film, The Aeronauts, starring Eddie Redmayne and Felicity Jones. Set in 1862, it follows groundbreaking meteorologist James Glaisher as he makes a record-breaking ascent in a gas balloon, to gain insights into forces influencing the weather.

Last year, Keith Moore, Head of Library at the Royal Society – the independent scientific academy of the UK – criticised Harper's film for 'airbrushing' Glaisher's male companion, balloonist Henry Coxwell, out of the story. 'I wanted it not to be two middle-aged men in a basket,' shrugs Harper, when we meet in London's Rosewood Hotel. 'I wanted it to be reflective for a contemporary audience.' He and screenwriter Jack Thorne replaced Coxwell with Amelia Wren, a fictional character inspired by Sophie Blanchard, a real-life aeronaut and daredevil pilot who died when Glaisher was just 10.

Complaining that Coxwell's bravery – he saved the flight at one point when the balloon began to fly upwards uncontrollably – was being overlooked, Moore commented to The Daily Telegraph, 'There were so many deserving female scientists of that period who haven't had films made about them. Why not do that instead?' Evidently peeved by the comment, Harper retorts: 'It's true. There were female scientists around at the time, but not in the Royal Society, because they weren't allowed in the Royal Society until 1948 or something, and even to this day, only eight percent of the Royal Society is female.'

It raises an interesting point: whether to sacrifice biographical authenticity for diversity's sake. Harper, 39, has more than paid his dues directing male-oriented stories – from Peaky Blinders to War & Peace. 'In War & Peace, there is Natasha, Sonya and Marya, but most of the meaty roles are men,' he notes. 'If you're looking at period drama, and period stories, there is a significant bias towards men. I think in order to tell stories for contemporary audiences that are relevant to now, where possible we should be seeking to address that balance.'

While The Aeronauts may bug those seeking an accurate history lesson, there can be no denying its positives. Reuniting Redmayne and Jones – who respectively won an Oscar and was nominated for one on Stephen Hawking biopic The Theory of Everything – Harper also got to push the technical boundaries. He and his team figured out everything from how to 'create clouds in a studio that look believable' to crafting a working 19th century gas balloon.

Somehow, Harper and co. even got Jones in the air performing stunts. How did that work with the insurance company? 'I'll save you from those conversations,' he smiles 'but I have to say I was amazed that we got to do what we did.' In the end, he achieved what he set out to do: a story about pioneers. 'They were taking these extraordinary risks to further human knowledge and to see the world differently,' he says. 'That was the real inspiration for the film.'

General release from Mon 4 Nov.