Film: The Aeronauts, a film of hopes and dreams

It's been nearly five years since The Theory Of Everything co-stars Eddie Redmayne and Felicity Jones appeared on screen together – and now they're teaming up once again for biographical adventure, The Aeronauts.

The epic - directed by Tom Harper and co-written by Harper and Jack Thorne - tells the tale of two high-flying balloonists, pioneering meteorologist James Glaisher and daredevil pilot Amelia Wren, united in a record-breaking voyage in Victorian England.

And nothing says 'reunion' quite like filming 70% of your scenes in a confined basket, reveals the British duo.

"It's just been fantastic, hasn't it?" begins Jones, 36, looking to Redmayne. "We built up so much trust from doing The Theory Of Everything, that it felt like we hit the ground running.

"We were in a really tiny space for really long periods of time, so it was good to be working with someone who you really respect and admire."

"We didn't know each other that well when we did Theory - and then we became very close making that film," follows Redmayne. "It really didn't feel like going to work for me, but it may have been different for her!"

"Eddie and I are like boxers," Jones compares. "We were so happy to be back in the ring together; we really push each other, constantly trying different things, not stopping until we've got something we're both happy with.

"It was great coming back to work with someone with such a familiar working method."

Redmayne, 37, agrees: "It's so rare that you get to push an actor in different directions and have the comfort of having great love and admiration for them.

"We have needed our mutual trust of one another to really push each other, and my God, we have needed it!" he admits, with a smile. "This film was nothing if not intimate and intense. Poor Felicity! It has literally been like having to live with me in a tiny basket for many months!"

Set in 1862, the balloonists' mission - and they certainly choose to accept it - is to advance human knowledge of the weather and fly higher than anyone in history.

But it's not all plain 'sailing' - for while attempting to further scientific discovery, the pair face physical and emotional challenges in the thin air, as their ascent soon becomes a fight for survival.

Suffice to say if you don't like heights, you'll be watching through your fingers.

For after building a fully functioning replica of a 19th-century gas balloon (the filmmakers reached out to renowned aeronautical engineer and pilot Per Lindstrand), thoughts turned to taking flight. For real.

"The thought was, the more we can do it for real, the more realistic it feels," reasons Harper, who from the outset wanted the experience to put the audience inside the basket.

In order to accomplish that, as much filming as possible was captured in the air - even down to the most death-defying scenes, including one where Amelia (Jones) climbs up the outside of the balloon.

Completing stunt work at height required a leap of faith from Jones, who found herself reunited with her Rogue One: A Star Wars Story stunt double, Helen Bailey.

And after weeks of stunt rehearsals and training with an expert aerialist, the actress was ready to take her performance to the skies; climbing the replica balloon's ropes at 2,000 feet, and pulling herself up from the basket and onto the hoop.

"The most important thing you need to know is that Amelia goes through many more physical extremes than James," quips Redmayne. "Felicity's physicality is formidable in this film; she is so hardcore and robust that it puts me to shame.

"[She] was sort of swinging up and down in the ring!" Redmayne remembers. "From my point of view it was quite terrifying, but she seemed at ease with it!"

"I would try and do as much as possible, myself, probably to my own detriment!" she says. "I think actually both of us were covered in bruises!"

Would Redmayne have given it a shot too?

"There's something so euphoric about it" he answers carefully. "Balloons have always been an object of fascination."

He recalls: "We were flying over Oxford one morning and people would be looking up and waving at us.

"The element of not knowing where you are going to land, of having to throw yourself slightly into the void, is why people find them so mesmerising. When you are landing a balloon, you just look for a field with a gate and hopefully no livestock and wish for the best!"

"Yeah, it's an amazing experience. And you have no idea what's going to happen once you're up," Jones mirrors. "It's a bit like a metaphor for life, you never know where you're going to land or what's going to happen, so you really are at the mercy of the elements.

"This could be a new way of travelling - you could 'get the gas air balloon'."

More than just incredible stunts and hypnotic flights, however, the process left both actors with a sense of awe about both humanity and our planet.

"Even though it's set in the 19th century, we're in a world in which we're all looking down at phones and at computer screens," muses Redmayne, who is currently filming Aaron Sorkin's The Trial Of The Chicago 7.

"The Aeronauts for me is a film about the freedom and the wonder of looking up. It's a film about defying expectation and refusing to be boxed in by society," he concludes. "So it felt like a kind of lovely hopeful feeling."

"It's a film about hope and feeling that anything is possible," asserts Jones, who has lent her voice to 2020 release, Dragon Rider. "In these times, which are increasingly becoming more complicated and worrying, it's great to have a film that is about optimism and to remind people that humans are capable of great things when they put their minds to it.

"You do leave it, hopefully the audience will feel, on a bit of a high," she finishes.

"There's a classic Hollywood ending in some ways and there's real joy in it and adventure – we definitely need a bit of light-hearted relief at the moment."

The Aeronauts is in cinemas now.