Actor Eddie Redmayne on his role in Les Misérables

“I often get bollocked for pouting but I’m afraid it’s just that I have incredibly oversized lips and if I shut my mouth...”

He duly closes his mouth to demonstrate. They are indeed massive lips. Combined with freckled skin, sandy hair, pale eyes and the obligatory jutting cheekbones, they give him a look that is at once stock handsome young actor and decidedly unusual.

It’s a jolie-laide sort of beauty, one which enchants his female fans (the “Redmayniacs”) and casting directors alike. In short the 30-year-old English actor is pretty enough to play very British heart-throbs in very British period dramas, but gnarly enough to take on much stranger roles.

In the former category are Angel in Tess of the D’Urbervilles, Stephen in Birdsong (both BBC adaptations) and Colin Clark in last year’s My Week With Marilyn; in the latter, a paedophile in 2011’s Hick and a troubled young man with Oedipal tendencies in 2007’s Savage Grace.

Then there’s his stage work; his performances in Twelfth Night, Richard II and The Goat, or Who is Sylvia? were all critically-acclaimed while his supporting turn in John Logan’s Red saw him picking up a Tony and an Olivier Award.

His latest project sort of straddles both categories. He is at once love interest and revolutionary in a role that is sweeping, epic, blockbusting and rather offbeat; that of Marius in Tom Hooper’s (he of 2010’s Oscar-winning The King’s Speech) take on Les Misérables, the musical adapted for the stage from Victor Hugo’s epic tome set in early 19th-century France.

This is, he says as he sits down opposite me in a swags-and-tassels London hotel suite, the biggest press junket he has ever been involved in. He adopts a look of bewilderment. Really, it doesn’t get much bigger than Les Mis.

The adaptation stars Russell Crowe, Hugh Jackman, Anne Hathaway, Amanda Seyfried and Helena Bonham-Carter. The stage show is the longest-running musical of all time and has been seen by more than 60 million people in 43 countries. Redmayne is one of them.

His parents took him and his siblings to see the stage production when they were children and family holidays were punctuated with Les Mis re-enactments in the back of the car for years. The young Redmayne was after the part of cheeky urchin Gavroche. His brother James took the central role of Jean Valjean.

“A lot of people love Les Mis,” he says with a raise of the eyebrows that suggests he finds the stats a little intimidating. “There is a massive sense of expectation. I loved it as a kid and I still love it. So there was this weird thing of going into work and each day I’d sing a song that I’d grown up listening to. I knew that it’s going to be on an album somewhere and that potentially another generation of people might listen to that. So there was a mixture of the weight of expectation of the 60 million people who’ve seen it coupled with my own expectation because I am one of them. The stakes felt formidably high.”

He can relax. Early reactions from critics have been positive and an Oscars buzz is already building thanks, in part, to the cast’s vocal performance. Since the original – written by Claude-Michel Schönberg and Alain Boublil – is a “sung-through” musical (ie almost all of the dialogue is sung) Hooper took the unusual decision that his cast would sing live on set rather than lip-synch to studio tapes.

The performances are more raw, more visceral as a result. The approach allowed Hooper, he said in a question and answer session following a screening, to “give the power back to the actors” and “pull the songs out of their souls”. In short, the actors (though many of them, Redmayne included, have surprisingly impressive pipes) could focus on the acting.

Both Hugh Jackman and Amanda Seyfried have experience singing on screen and both intimated to Redmayne that when singing to a pre-recorded track, much of your brain power is focused on simply making sure your lips are moving at the right time and in the right way. Such an approach, he says, “certainly means that you cannot be instinctive.”

“Acting on film,” he adds, “the greatest stuff comes from a place of spontaneity, of listening to what the other person says and reacting to how they communicate, so I found it wonderful working this way. Health-wise it was rigorous because I just cared so much about my vocal health. That sounds silly but despite this set being filled with Wolverine and Catwoman and Gladiator, there was a huge amount of lemon and honey vaporisers...”

He may have wanted to play Gavroche as a child, but from the beginning it was the role of Marius – the handsome, idealistic revolutionary who falls in love across a crowded street – which drew him to this project.

He was filming Hick in North Carolina when he heard that the film was being cast. Dressed as a cowboy, on a night shoot and with a couple of hours to kill, he filmed himself singing Empty Chairs and Empty Tables – Marius’ signature song – on his iPhone. The recording ended up in the hands of the film’s producers and a rigorous audition process followed because Hooper was aware that few actors could convincingly sing to camera for 12 hours a day.

“All the actors were put through the mill because Tom knew that he was doing it live and there had to be this stamina. [The audition process] was like this X Factor-style panel of judges. I have a new-found respect for the people who go on those television programmes.”

His family – all Les Mis geeks of sorts – were desperate for him to land the part: “My older brother James doesn’t have a theatre or music background at all. When I was auditioning for this I really wanted it but James... I’d get text messages every five minutes: ‘have you heard? What’s happening? What’s the latest?’ And when I eventually got the part my family were so happy. I had my first singing lesson at my parents’ home and Tom Hooper came to check how it was going. And my family are such obsessives that James’ wife Emma – who is also a massive fan – brought in my new-born niece and asked if there was a part for her...”

Inspired in part by those early family visits to the theatre, acting was an early goal for Redmayne. One of five, his was a privileged upbringing; he comes from a family of bankers and grew up in London, attending first Eton (he was in the same year as Prince William, much to the excitement of the US press) then Trinity College, Cambridge where he got a 2:1 in art history (his “back-up” option).

His vocal abilities may come as a bit of a surprise to some fans, but there are recordings of him on YouTube singing solo with the choir at Eton and indeed he does have some experience in musicals. He first appeared on stage aged 12 in Sam Mendes’ production of Oliver! playing “workhouse boy number 40”. He sang and acted at school and university, performing with the National Youth Music Theatre, and at 18 he travelled to Edinburgh for a production of Cabaret on the Fringe.

“Half of my family live in Edinburgh,” he explains. “My grandmother’s in Liberton and the last proper musical I did was Cabaret. It was in the Underbelly and it was all dark and dingy. I remember my cousin brought my grandma to see it and we were all in latex, PVC and masks and there was quite a lot of interaction. I was up in my grandma’s face and I just heard her say ‘and when is Eddie coming on?’ And my cousin was like ‘that’s him! The one leering in our faces!’”

He claps his hands together with a laugh. He is all excited enthusiasm and schoolboyish charm, talking with eyes wide and hands animated, always terribly, terribly polite. He looks significantly younger than his 30 years and he seems it too, as if at any moment he might be getting up to jolly japes behind his house master’s back.

Perhaps it was that air of gilded youth combined with a very specific sort of boyish Britishness which inspired Christopher Bailey, the creative director of Burberry and a supporter of the arts, to approach him to become the face of Burberry Prorsum, the brand’s catwalk line, an experience he describes as “totally surreal and completely odd”.

“I’ve got some hilarious photos from my brothers in different parts of the world up against a billboard mocking my Blue Steel” he says with a laugh, pulling the famous male model pose from Zoolander by way of demonstration. His brothers may tease him, but there’s no doubt that he’s become something of a style icon over the past year or so. In September, Vanity Fair included him on its annual best-dressed list, and today he’s rather dapper in a blazer, shawl cardigan, pale-blue T-shirt and silk socks in the same hue.

As filming on Les Mis progressed, it became apparent that of the dozens of actors playing fellow revolutionaries alongside him, a significant chunk of them had played Marius on stage. Wasn’t that more than a little intimidating? He smiles. “Obviously I was instilled with fear and I assumed that every time I opened my mouth everyone was thinking ‘oh you’re going to do it like that?’ but they were incredibly supportive and after a while I would ask them for advice. ‘How did you do that? And this bit?’ And try to glean all their best bits. So it was helpful, really.”

Despite their extensive experience, what was new for everyone on set was the idea that they would be singing all day, every day, hence all the honey and lemon vaporisers. Performing two shows a day on stage is a tall order. Singing from 5am-8pm is on a completely different level, “like retraining everyone’s vocal cords to be marathon runners, really.” It took him 21 takes to get Empty Chairs and Empty Tables down, and it was the 21st take that made it in.

He uses the word “rigorous” more than once, and filming such an epic spectacular (it’s nearly three hours long) was nothing if not demanding. “One of the most enjoyable, frenzied moments of the filming was building the barricade,” he says excitedly. An iconic scene, the barricade is hastily built by students and peasants to stave off the authorities using bits and pieces of furniture, and few can fail to be roused by the sight of them singing Do You Hear the People Sing? atop it.

“Tom had 60 peasants and 30 students and he got five camera men dressed as peasants, put in ten minutes worth of film stock and said ‘right, build a barricade. Action.’ We were like ‘what?!’ Suddenly there were pianos and wardrobes falling down from all these shops, these detailed sets, we were literally just taking anything and we built a barricade in ten minutes. The anarchy and the adrenaline; my inner seven-year-old was having the best day of his life.”

He grins a grin that’s disarmingly wide before being ushered off to his next appointment on this worldwide junket. With Les Misérables set to be one of the biggest international releases of 2013 that distinctive mouth – pouty, pretty, obscene – is about to go global, and the name Eddie Redmayne will be on everyone’s lips.

• Les Misérables is released on 11 January.