Firth, actually       Millions of women fell in love with Colin Firth when he emerged wet and tousled from a pond as Mr Darcy. It seems to be an image he can't shake off.

Look, there he goes sideways off a jetty, wearing a large jumper, joining the pond life in his new film, Love Actually. "That was pretty disgusting, actually. The problem wasn't the cold. The problem was that is was mostly mud. Really, really nasty." And who among us can forget his graceful swan dive into the pond in Pride and Prejudice in tight white breeches? A pond, he says now, that was full of indignant frogs and nasty pond stuff: "It was very, very filthy and unhygienic."

Colin, wet and tousled, is a romantic image, no two ways about it. Colin wet and glowering as Mr Darcy, striding across his magnificent estate in the BBC television series, was a powerfully stirring moment. "Nobody on the set—nobody—had any feeling that anything particularly sexy was happening," he says of the scene that launched him into the fevered fantasies of millions of women.

Colin, dry, is sitting in the Dorchester hotel in London, awkwardly wrestling with a huge and uncontrollable club sandwich. With very short hair and wearing severe black glasses, he is intense and serious. Tall, with amazingly healthy skin, dressed in expensively tailored black, he is intelligent and as darkly handsome as you would expect. Better in person that on the screen, in fact. Taken together, he and Hugh Grant represent the current comely face of British film.

Now filming the second Bridget Jones movie, where he plays Mr Darcy for the third time, he is the more sombre foil for the flashier and more mercurial Grant, who always gets all the good jokes, according to Firth. "I find it quite extraordinary how much more famous he is than most other people, when it comes to our profession," he remarks. "I went to Los Angeles to do publicity for Bridget I, and I don't know if I have ever felt quite so invisible. Coming out of the airport with Hugh, going through all the red tape and immigration and so on—everybody knew him. Any by the time we arrived at the hotel, the VIP treatment he got at the expense of absolutely everybody else around—I mean, I could have lain bleeding on the carpet, and they would have stepped over me to help him with his bag." Indeed, quite a lot of people would leap at the opportunity to punch Grant, push him into a cake and throw him through a window, as Firth did in Bridget Jones. Decking Grant was something, he admits wickedly, "I have been wanting to do for years"

Helen Fielding, author of Bridget Jones's Diary, was so enamoured of Firth in Pride and Prejudice that she had him in her mind when she created a modern Mr Darcy in her books. She carried the joke further when she had Bridget—briefly and disastrously working as a profile writer for The Independent newspaper—go to Rome to interview Firth, specifically and obsessively about the pond and the wet shirt. Try as she might, Bridget could not think of any other questions. (I can relate to that) So it is a kind of ironic joke that Firth appears in the Bridget Jones movies, though there could not have been anyone else in that role.

Though Mr Darcy is almost a Mills and Boon romantic hero—an abrasive anti-hero who turns out to be the good guy in the end—Firth would not describe himself as a romantic. "I don't think I am really, particularly, no. I am not romantic about life," he says, then after some consideration leaps to his own defence with a flourish, "I am romantic in the abstract!"

This is the second time I have met Firth. The last time he was in Luxembourg, busy playing the Dutch master painter Johannes Vermeer in the beautiful film Girl With A Pearl Earring, which opens in Australia in January. Then, as now, I was struck by how his dimpled smile transforms his natural glower into something approaching delight. Based on the book by Tracy Chevalier, Pearl Earring is the story of how the master came to paint a lowly servant in his house, for what was to become perhaps his greatest masterpiece—the luminous painting for which the film is titled. A film of few words, the forbidden and repressed sexual desire between the painter and his subject (played by Scarlett Johansson) is conveyed through loaded glances and electric touches. Ladies will love his smouldering portrait of an artist, all sexy-grumpy in a long wig, lace collars and moody moustache. Filming was going well and in that encounter Firth was relaxed, amusing, giggly, conspiratorial and forthcoming—a side of himself he does not always display to strangers, being a reserved sort of chap by nature, though perfectly polite.

Immersing himself in the art and life of Vermeer was clearly a most satisfying way to be making a living: "I loved going to galleries and being that bloke." Firth intellectualises his roles, takes them apart and examines them from all sides, prepares and researches. "That is the greatest perk of the job, probably," he says from the other side of his sandwich. "It is a licence to have fun and plunge into a different universe. With actors, as long as you have got that sort of thing available to you, life can never really be totally banal.

Opening in Australia on Boxing Day, Love Actually is the eagerly awaited, enormously ambitious directorial debut of the writer Richard Curtis, who as a screenwriter brought us Notting Hill, Four Weddings and a Funeral and Bridget Jones's Diary. In so doing, he reinvented British cinema to reflect contemporary middle-class England—well, okay, his mates who live in deeply fashionable Notting Hill. Five films in one, Love Actually explores the variations of love in five interwoven stories. It is an ensemble film with an all-star cast and some powerful performances. It somehow combines tragedy and comedy in a seamless, feelgood whole, even if it does stretch credibility at times—like Hugh Grant's prime minister falling in love with the tea lady. Firth's character, a writer, has caught his girlfriend in flagrante with his brother and has retreated, wounded, to the south of France, where he falls for the Portuguese girl who comes to clean his house. Because she speaks no English, and he no Portuguese, their growing attachment is conducted in subtitles. "I am married to an Italian, so I know the helps and hindrances of the language barrier. I think maybe these two fall in love because they can't understand the silly things each other is saying."

When Firth met his wife, Livia Guiggioli, 32, a film producer, on a film set in Colombia in 1995, she and her family greeted the news that he is a sex symbol in Britain with incredulous laughter. "Well, she found it incredibly unlikely. Her family thought it was inconceivable, actually. Italians don't find reserve sexy." And yes, since you ask, he is bloody sexy; both he and Hugh Grant, in person, are almost an assault of polished, freakish male beauty and brains. But Firth says his heart-throb public image has no bearing on his life. "It doesn't even exist. Until it is mentioned, it is usually associated with the press or something—it is a story-related thing. But I don't hear it at home, believe me." He has said in the past that he is very happily married, that his family brings him peace and tranquillity, and that if he needs advice about work he talks to his wife. "She is the smartest person on Earth. She is much more secure than I am."

Even though it might appear to some people that Firth's reticent glower does not change a great deal from film to film, it is not because he is not trying. He admits that he has found a niche as the tense, repressed Englishman and now is generally required to do variations on that theme. But his immersion in each role can be an ordeal, nevertheless. And can take over his life in a rather harrowing manner. He is, I suspect, quite sensitive and earnest. When I comment that pretending to be other people is an aberrant and odd kind of job, that making a living from being histrionic is not really normal, he readily agrees. He tells a long story about how two of his friends once swapped lives for a month as an artistic experiment, and wound up being psychologically damaged. There are clearly pitfalls here to acting as a different person every time you go to work. Is there something fundamentally wrong with people who choose to do this, I wonder?

"You know, entering into a different life is going to have an effect on you, I think. I will tell you one thing— it isn't reliably therapeutic. I think it is very dangerous to think it might be, that it can help your life. You can go somewhere, and there is absolutely no kind spirit helping you back from it. I think you just take that risk when you do it." He believes there is "something wrong" with spending months being someone else. "I think actors are essentially juvenile. There is a retarding element to the job, and I also think that it is very difficult to do it brilliantly unless your ego is somewhat fractured. I think you have got to be a little unstable, probably. If you are very grounded, and have got a very firm sense of who you are, how do you tip up the balance in order to be someone else, and then go back to this firm, grounded person? I don't really think it is possible. There have got to be some screws loose somewhere."

Firth's screws appear to be firmly in place, by and large. With a slightly nasal, flat London accent, he seems sane, low-key, agreeable, with no visible tics or tremors. Perhaps this is because he has ordered his priorities, and they do not involve poncing around being a star. He is a solid family man whose life revolves around his three sons—three-month-old Mateo, Luca, aged three, and Will, 11. Will lives with his mother, the actress Meg Tilly, in Los Angeles, with whom Firth once disappeared into a log cabin in the wilds of British Columbia for several years until cabin fever set in and he beat a retreat. He takes long breaks from filming in order to visit Will, be with his family in London where he lives, and to achieve some kind of balance in his life.

"I enjoy my personal life. Making a film is so all-consuming that very often your family get to see very, very little of you. You will only have a Sunday off, and if you are luck enough not to be away on location you will be able to see your family. So I tend to cherish the times in between the work, and doing absolutely everything that I suppose most people do with their evenings and weekends. When you have kids, nothing else really matters. I love the idea of a break after a film. I think if you are going to do the job properly you should recover from one, shake it off and have time to prepare your mind for the next."

His announcement at the age of 14 that he intended to become an actor was met with a curious silence. There was absolutely nothing in this family background that would point him towards the stage. "The day before I thought it, it was inconceivable. It just suddenly occurred to me. I just didn't enjoy anything else very much."

All four of his grandparents were Methodist missionaries in Africa, which may account for a kind of austerity about him, and the rest of his family are energetic academics. Born in 1960, he spent his early childhood in Nigeria. It was a bookish household, without television, with parents who were both social activists working on behalf of asylum seekers, among other causes. As a young man, a guitar-strumming Firth displayed left-wing zeal, orange flares and long hair. Though he calls himself a "passive resister", to this day he works for worthy causes and has much to say about asylum seekers, and how humanity and compassion should not have anything to do with national borders. He initially turned down Pride and Prejudice because it was too "mainstream", but is over that purist phase now.

Last time we met, he admitted that by going to acting school rather than university he always felt something was missing, that he could never quite catch up. "My father was at Cambridge, his father was at Oxford my sister went to London, my mother was at Nottingham, and all my cousins and extended family are brilliant achievers in the academic world, and I think there is a part of me that always feels a bit like the dunce. My parents are still working relentlessly—travelling, teaching, learning, conferences, far busier than I ever am." Even so, his father, a history lecturer, reassured him that dressing up and acting like a Jane Austen character was a study of a literary text that was possibly more effective than writing essays. His brother Jonathon is an actor, his sister Kate a voice coach.

Mr Darcy in his wet shirt is, he says, a kind of hologram that hovers around doing things without him, even though "I was delighted to become a popular culture reference point. I'm still delighted about it actually, and I still find it to be weird. I left him behind the day I walked off the set." Some people, however, get a bit of a shock when they find Mr Darcy sauntering around the supermarket and momentarily forget their manners. "I am not going to get someone to do my shopping for me. I quite enjoy doing things for myself, but I just don't particularly like somebody standing behind me getting on their cell phone and telling their friend that I am buying bog roll. And what is a bit strange is that some people are so amazed to see you in a place like a supermarket, they just laugh and shake their heads—particularly guys. I have seen that head-shake a lot now."

Although he is best known for romantic comedy, he likes a departure into drama—"Pearl Earring was very welcome for this reason"—and he has just finished filming Trauma, "a sort of horror film", with Mena Suvari. "I made it with a wonderful director called Marc Evans. It is about a man who wakes up after a car accident in which his wife was killed. His grief is complicated by the fact that that very day, someone very famous has died, and the whole nation is in mourning. It is about his loneliness and isolation, and trying to make sense of everything, because his memory is vague.

"It was an interesting study. I don't know what is going to come out in the wash, but I think it will be an extraordinary film. I found it very strange to change conventions, to change genre and realise that none of this stuff has a twinkle in its eye or its tongue in its cheek—this is earnest. We have to mean it."

Now, would someone please throw this man in a pond.