It was almost two years ago that I first met Tom Hooper. He was with Colin Firth, and their film, The King's Speech – which Hooper directed and in which Firth starred – was weeks away from winning its Oscars. It was a heady occasion. An excitable Hooper did most of the talking (Firth detests interviews) and the film – about the struggle George VI had with his speech impediment when he came to the throne in 1936 – became the unlikely winner that delighted everyone who saw it: an impossible act to follow.

And yet, today, Hooper is attempting to trump it on an epic scale. He has taken on Claude-Michel Schönberg and Alain Boublil's colossus of a musical, Les Misérables, which has been seen by 60 million people worldwide. And he has the big guns out in force: Hugh Jackman, Russell Crowe, Anne Hathaway. The cast even boasts Sacha Baron Cohen for comic relief.

When I last saw Les Misérables in the West End it seemed past its prime. I had not expected to enjoy the film at all. Yet what Hooper has achieved is close to miraculous: he persuades one it is perfectly normal to sing one's way through French history. He has replaced sentimentality with sentiment. The film looks – and sounds – splendid: West End frumpiness has gone for good.

It is mid morning and Hooper is perfectly dressed for Claridge's, which is where we meet. He sits over his coffee, looking every inch (at 6ft 3in) a gent, wearing an eye-catching black velvet jacket. Everything about him is tailored, from his conversation to his haircut – a neat sweep of fair hair combed from a side parting. What I want to know is how he is feeling at the end of his marathon? How was the premiere? "It felt like a deliverance," he says, "and as I was sitting at the Empire, Leicester Square, I remembered going there as a kid. I used to have a ritual: I would stand in the doorway and make a commitment that one day I'd have a film of my own in that cinema. I still feel very much in touch with that 12-year-old."

As he speaks, Hooper stares over the edge of the hotel armchair at the carpet as if it might yield some answers. He seldom looks at me directly. The sense throughout is that I am not quite meeting him at all, that the conversation he is having is with himself. And one wonders how far this is an occupational hazard. His job, after all, is daunting. He tells me he oversaw "1,000 people" and saw his role as "parental". But Russell Crowe – who plays the murderous French policeman, Inspector Javert – has been quoted as saying that Hooper is not so much a parent as a "tough guy. When he wants something he wants it and he is going to have it."

Hooper's response to this is that there is a need for toughness, especially when managing a $61m budget. He talks about moments when only he could decide whether dishing out "another £500 or £700 was necessary". And he sounds as if he is trying to convince himself when he concludes: "The way you spend money is creative."

So how would he identify his faults as a director? "When I was in my 20s [he is 40 now] I was too hard – I got tunnel vision. I used to forget to thank people. I have got better at being gentler and more generous, remembering people need compliments to energise them."

As if to prove he has learnt this lesson, he launches into a speech about Hugh Jackman who stars as Jean Valjean. He describes him almost as a latterday saint who "led" the cast. The impression one gets, reading between the lines, is that the making of the film must often have been a nightmare. Hooper admits "the hours are long and can be very brutal". Anne Hathaway and Hugh Jackman, in particular, could have been forgiven for feeling below par. Both went on drastic diets to make sure Les Misérables was miserable. Hathaway lost 25lb – and her gorgeous head of hair – to play Fantine. Jackman lost 30lb "to create the physique of the convict… I thought this was going too far, I was worried about safety. It was freezing cold and his skin went like paper and wrapped back on his bones – he looked so extreme."

He then drops into the conversation that he "recently watched the film in LA with Barbra Streisand" who told him she didn't recognise Jackman for the first 10 minutes. "I loved that… Hugh's instinct was smart: he understood that achieving a shocking level of realism would help to bed-in the live singing."

Live singing is what makes the film. It is also doing things Hooper-style – the hard way (usually, the singing in films is dubbed). Hooper told his cast: "Forget that these songs are globally iconic and try to reinvent them." He explains the technical side: each actor had an earpiece through which they could hear an electric piano. The crucial thing was that they could choose when to start singing: "Eddie Redmayne singing Empty Chairs… had to find the perfect moment emotionally. He could sit for 20 or 30 seconds until he got there in his head."

The other thing that makes the singing so powerful is the use of close-ups. In Anne Hathaway's I Dreamed a Dream her face becomes the song. Hooper (again keen to give credit) insists the idea was Redmayne's: seeing footage of Hathaway's face, he wondered: "Could you hold an entire song on that?" The answer is the film's high point.

"Eddie is a friend," Hooper says. "I trusted his instinct."

It is harder to picture Hooper collaborating with Sacha Baron Cohen (alias Ali G, Borat and Brüno) – if only because Baron Cohen is so used to directing himself. How did that pan out? "I loved working with him. We share a bordering-on-obsessive perfectionism. No one knows how rigorous he is about comedy…"

Baron Cohen plays Thenardier, an uncouth inn-keeper, with Helena Bonham Carter as his disgraceful other half, and is anarchically funny. In my favourite line, he mispronounces "Cosette" in an improvised adieu: "Farewell Courgette." I don't remember this from the musical? "No, he made that up. He'd be pleased you like it."

But when I reveal that I never cared for the stage version, Hooper reacts to this heresy as if he had gone selectively deaf. Later he waxes eloquent about the story's timeliness: "There is so much anger in the world, with rising economic inequality, social inequity, protests on Wall Street, protests outside St Paul's and riots… and seismic changes in the Middle East… Revolution is in the air."

Les Misérables is "the great anthem of the dispossessed, the cry from the heart of those who suffer". He approves of its message: "Through collective action we can do something." Its specific prescription? "Start by loving the person next to you."

Actually, though, he talks more about Victor Hugo's 1862 novel than the musical – he lent on it for inspiration and was gripped by Hugo's obsessive eye: "We were fellow travellers in our love of detail," he says, although he admits that when Hugo devotes 20-30 pages to an exhaustive exposition of the Parisian sewer system, "I had to skip a bit".

It makes sense that Hooper would want to go back to the book. His education has been literary. He grew up in London and went to Highgate school where he was inspired by ex-RSC actor Roger Mortimer who taught drama. He decided against film school in favour of reading English at Oxford: "I had already learnt a lot of the technical stuff and felt I needed to spend three years on ideas, stories and dramatic structures."

He directed plays at Oxford (his contemporaries included Kate Beckinsale, Emily Mortimer, Eve Best and Tom Ward). He shot commercials (breaking off from finals to make a Sonic the Hedgehog ad with Right Said Fred). After university he worked on TV soaps (EastEnders, Cold Feet, Byker Grove) and period dramas (Love in a Cold Climate and Daniel Deronda). But it is his collaborations with screenwriter Peter Morgan that stand out: the superb BBC drama Longford – about Myra Hindley – and the film The Damned United with Michael Sheen as football manager Brian Clough.

Yet what we dwell on is his first success, Bomber Jacket, which won a runner-up prize in a BBC young film-maker competition. It was about his grandfather, a Lancaster bomber navigator, killed in 1942, aged 30, and an exceptionally sophisticated film for a 14-year-old to make. Later he would dedicate The King's Speech to his grandfather's memory. "I have always felt affected by my dad not having a dad, and felt very sad for him," he says.

Family matters to Hooper – it is one of the most likable things about him. His father, Richard Hooper, was deputy chairman of Ofcom and has more recently been in charge of the Hooper report on the future of the Royal Mail – commissioned by Gordon Brown and taken on by David Cameron. His pride in his father's achievements is evident. When describing his Australian mother, Meredith, he is in danger of drifting right off task in the direction of Antarctica (a continent about which she is something of an expert) while at the same time championing her latest book, The Longest Winter: Scott's Other Heroes. Which parent does he take after? "Both," he says. He gets his "drive" from his father. "His work focus is prodigious. When I was growing up, if I went into his study, I could stand there and go: Dad… Dad… Dad! And he wouldn't hear, he would be so inside." From his mother, "I've learnt to be brave and inhabit uncertainty and not just look for instant decisions. Where she is brilliant is when you ring her up and ask for advice, she will – more often than not – say something lateral. I love that."

It is interesting that he prizes uncertainty – he seems so certain about everything. What he also reveals is that it is through his mother that he comes by his affection for Australia (and his enthusiasm for antipodean actors – Hugh Jackman, Geoffrey Rush, Russell Crowe). Although he seems as English as you could get, he does not want his Australian roots forgotten. He was gratified recently when an Australian producer told him he had what it took to direct an epic because "you have a big landscape behind you".

There is no question that he thinks big – but does he understand what drives him? He hesitates. He wants to produce work that is "as good as it can possibly be". He is not about to rest on his laurels, or to rest at all. Then he adds: "The funny thing about being a director is that you are not seeking your own pleasure. Your own pleasure is beside the point – it is deceptive. A lot of the time when you shoot, you are pained. It is quite masochistic – you have to be in touch with your unhappiness because that is part of the early radar system that tells you when something isn't working. So you go between unhappiness and joy. It is what is in the frame when you turn over, that is all that matters.'

Does he know what he will direct next? He says: "I've no idea, I've not had any time to read a script."

I ask about his private life. "I don't have one," he replies, quick as a flash. He volunteers that the last time he had a day off was last summer. And what did he do with it? "I slept."

Les Misérables opens on 11 January