Media playback is unsupported on your device Media caption His Dark Materials: Lin-Manuel Miranda shows us behind the scenes

Ahead of the eight-part dramatisation of the first of Philip Pullman's best-selling His Dark Materials novels, the BBC's Sian Lloyd describes her sneak-preview behind-the-scenes set visit earlier this year.

Huddled around braziers filled with warm coals or sitting with blankets wrapped over shoulders, close to a hundred shivering extras are trying to keep the cold at bay.

They are the Gyptians, the nomadic closely-knit boat-dwelling tribe at the centre of Pullman's trilogy, who are about to get some disturbing news.

In the real world, we're on the site of a former ironworks in Blaenavon in the south Wales valleys. There's snow on the ground, and temperatures are still plummeting.

Cast members and crew have gathered for the opening scenes from the series, which covers the events of the novel Northern Lights, and which receives its premiere in London on Tuesday.

The book has been adapted by the award-winning Jack Thorne (Shameless, Skins, The Fades) and filming has taken place almost entirely at locations across Wales.

The first book in the trilogy also had the Hollywood treatment in 2007. The Golden Compass starred Daniel Craig, Nicole Kidman and Dakota Blue Richards.

Image copyright Penguin/Random House Image caption Philip Pullman wrote three books in the His Dark Materials series

The fantastical story centres on a girl called Lyra whose sheltered life in a version of Oxford in an alternative universe is turned upside down by the arrival of the mesmerising but sinister Mrs Coulter.

Lyra, played by 14-year-old British and Spanish actress Dafne Keen, finds herself embarking on a dangerous adventure meeting giant polar bears, witches and evil villains,

Mrs Coulter is played by Ruth Wilson and Lyra's uncle Lord Asriel is played by James McAvoy.

Six months later, on a warm summer's day, another main cast member, the acclaimed Lin-Manuel Miranda, strides across a studio floor in Cardiff.

Image caption Dafne Keen plays the central character Lyra

The production has predominantly been filmed inside a former factory, which is now home to the 250,000 sq ft, state-of-the-art Wolf Studios Wales - and that's in no small part to the unpredictable weather.

Miranda, best known as the Tony award-winning creator and star of the musical Hamilton, leaps into a metal shell resting against a vast green screen.

"Welcome to my hot air balloon," he grins, explaining he plays the part of aeronaut Lee Scoresby, who he describes as a "Han Solo-type figure" who helps Lyra on her journey.

"When you see this on the screen, it'll be flying through the clouds," he laughs, all thanks to computer generated technology.

Image caption Lin-Manuel Miranda on set in his hot air balloon

The American actor describes himself as a huge fan of the Pullman books, which he first discovered in 2005.

His Dark Materials is made up of three novels; Northern Lights, The Subtle Knife and The Amber Spyglass. They've been translated into 40 languages and sold close to 18 million copies worldwide.

Miranda says he's thrilled to be part of the landmark series and didn't need to think twice when he was approached to play the part.

He describes every day's filming as "a new adventure".

Image caption One of the magical polar bear-like creatures on Lyra's journey

"Today I'm swinging in the hot air balloon, tomorrow I'm having a bar fight, tussling with stuntmen all day."

And while he says it's not the same buzz as performing before an audience, he says he's equally enjoying this experience.

"The energy comes from knowing we are not coming back to this, from being ever present because you know this is the day to get this done and that's the substitute to an audience for me," he says.

He's also enthusiastic about his time spent in Wales, having made Cardiff his home for months at a time - and delighting locals with regular appearances at a karaoke club in the Welsh capital.

This will be one of the most expensive dramas yet to be shown on the BBC. The cost, which isn't being revealed, is being shared with HBO, the US network which will distribute the drama internationally.

Image caption Ruth Wilson plays the villain of the piece Mrs Coulter

Jane Tranter, the executive producer of His Dark Materials and co- founder of the independent production company Bad Wolf, describes it as "the most challenging piece of work she has undertaken".

Tranter recognises that many of Pullman's fans have waited decades for this and says the production is staying true to the original books. "These are glorious works of literature, why would we want to mess with them?" she says.

Image copyright Reuters Image caption Dafne Keen says the story is multi-layered and "very deep"

But she adds that eight, hour-long episodes devoted to each book, will allow opportunity to delve deeper and further.

"Philip Pullman leaves these little threads in his work, where there is a hint at someone's back story, or a hint at what someone might be doing when something else is happening. We can pull at these threads and make a little more of them."

She describes working through the complex and deeply imaginative piece of work as a "hugely ambitious" feat.

Image caption Lord Asriel, Lyra's uncle, is played by James McAvoy

In Lyra's world everyone has a daemon, a physical version of their inner self which takes the form of an animal, which can appear alongside them or about their body.

Dafne Keen says the standout things for her about the story are "the main character is a young girl and that it goes very deep".

"If a nine year-old watches it they will only see the adventure, an adult will see all the layers… and it is very dark," she adds.

To help the actors perform, each scene is rehearsed with a 3D-puppet of the animal which has been painstaking created to replicate the CGI form that will be added in post- production.

Operated by a puppeteer, it allows the actor to get a sense of the correct space. The scene is then recorded without the puppet being present.

Ruth Wilson says one of the most compelling parts of the story was the daemons. "It is very unusual and different, an animal soul mate is an intriguing element for us all," she says.

Lee Scoresby's daemon is an arctic hare named Hester and Manuel admits he's become quite attached to the creature made from rope and foam, welcoming him on set like an old friend.

Overall, Manuel says he became engrossed in Pullman's work by its complexity and themes, adding "it takes on life and death, love and growing up and losing people".

Unusually, work is already well under way on filming the second series even before the first has been shown.

This, the BBC says, demonstrates its commitment to an iconic work which resonates with young and older audiences alike.

His Dark Materials begins on BBC One on Sunday 3 November.

Follow us on Facebook, or on Twitter @BBCNewsEnts. If you have a story suggestion email entertainment.news@bbc.co.uk.