Thoroughly modern Julie

Julie Andrews tells Emma Brockes about her stepfather's alcoholism, hitting Broadway at 19 and Dick van Dyke's terrible English accent.

When it comes to Julie Andrews, you either get it or you don't. Notice of my interview with her prompts two responses: uninterest bordering on hostility from my straight male friends and hysteria from everyone else. People scream and hop about and, throwing their eyes to the back of their heads, collapse to the floor. In a small, sad voice my best friend says: "Give Julie our love." "Aaaah," says Andrews. "That's so nice. Tell them I'm very grateful." She smiles, displaying perfect Julie teeth.

Affection for Andrews has grown in the 40-odd years since The Sound Of Music was made, to the extent that she is one of the few Brits to rival the status of America's biggest stars. With impeccable manners, she always attributes this to luck and to the fact that, because she is lodged in people's childhood memories, she is almost impossible to eradicate. It has also to do with a kind of sincerity: some stars survive by changing with the times; Andrews has thrived by resisting them.

Her new film, The Princess Diaries 2: Royal Engagement, attempts to bring Andrews into line with more modern entertainment values. It is the sequel to the 2001 hit based on Meg Cabot's fairy tale about a grungy American teen who inherits the crown to Genovia, a European state of which Andrews is head. The first film had a rough, joyful energy that is missing from the second, a thoroughly market-tested product. Six-year-old girls will love it.

"You know what, it's got some nice subtle messages," says Andrews crisply. "A lot of films seem to go to the lowest common denominator. And this one is talking about responsibility and growing up and assuming your destiny and your life and all of that. It's not a bad message. And being decent; being decent to people." She is very emphatic about decency.

The power of Andrews's early roles makes watching her in anything else unsettling, particularly now, given her failure to age in line with the rest of the population. She is 69 but could be 20 years younger. The director, Garry Marshall, tries to address this by making veiled references to Andrews's career ("I've done a bit of flying in my time," says her character at one stage, nodding to Mary Poppins.) It is Disney's little joke, and one, I sense, that Andrews does not entirely approve of. "It was just a nudge," she says, smiling gamely but with underlying waspishness. Her image is often mistakenly identified as sweet, but there is a steeliness to her that goes beyond the usual fortifications of the famous.

It is Andrews's voice that has defined her. It never came easily. She always had to warm it up and was envious of those who could burst effortlessly into song. "As my mother said, I never sprang out of bed with a glad shout. My voice needed oiling, and then it took off." Since a disastrous throat operation, eight years ago, Andrews has been unable to sing. But she speaks with the same precise delivery she brought to her songs. Her words are like beads of mercury: they don't run together. When she refers to Tony Walton, for example, her first husband and father of her grown-up daughter Emma, she pronounces "ex-spouse" with a pause in the middle, to distinguish the two "s" sounds. It has taken her 40 years of living in the US to cave in and pronounce "laugh" with the short, American "a". As she comes from Walton-on-Thames, in south-eastern England, it is always assumed that she has had elocution lessons. But Andrews's diction is the result of her singing lessons, on the foundations of which her whole manner is built.

It was her stepfather, Ted Andrews, who got her into singing, one of the few things she has to be grateful to him for. When her mother remarried she was forced for reasons of respectability to change her name. Her real name is Julia Wells. She used to imagine as a child that, if she grew up to be a novelist, she would combine her middle name with her real surname to sign herself Elizabeth Wells. Was her real dad annoyed about the name change? "I suspect he was. He was such a honeybun. He was a really decent, honest . . . a . . . a nature-loving man. He gave me the grounding. My mother gave me all the sort of chari . . ." She stops short of saying charisma, as if curbing an unseemly spurt of ego. "Flair, or whatever," she mutters, "and I don't hold a candle to her, she was wonderful. But my dad was the sane one, really. He treated the kids as beloved equals. He was a teacher and a good one."

Ted Andrews, by contrast, was a song-and-dance man and an alcoholic. The family was dysfunctional, she says, to the extent that in her 20s she had a lot of therapy to remedy the fallout from it. "They gave me as normal a childhood as possible, but it certainly wasn't . . . I didn't know what normal was in those days. I was working from a very early age. So I probably missed out on some of those things . . . . God knows every family has its problems."

I ask if her stepdad was violent. "Yeah," she says, "there were times when he was." There is a long pause. She sighs. "He was kind of a very sad man. I have to say I have great compassion for him, because he had a tough life himself, although at the time it didn't make much difference to me. You can imagine, I had this lovely dad, I didn't like my stepdad and I wasn't going to accept him. And I mean, he tried. But his demons got in the way. So . . ." Another pause. "Yeah. He wanted life to be better." What were his drinking patterns like? "He'd go sometimes for two years if we were lucky, and be completely sober, and then fall right off the wagon again. In those days there wasn't as much help. With absolutely no self-pity, I think I sort of was the glue that held the family together." It was an upbringing that made her if not intolerant of alcohol then at least very aware of it, something that helped her withstand the pressures of early stardom. It also, I suspect, made her tough. When Andrews was 19 she won the lead role of Polly in a Broadway production of The Boyfriend and flew unchaperoned to New York. Emotionally, she says, she was much younger than her years.

The contrast of Manhattan with Walton-on-Thames might easily have derailed her. But Andrews simply knuckled down and, true to the image that would later define her, got on with it. "The work was hard, I was learning my craft and floundering to stay . . . let's see if I can put it correctly and succinctly," she says, sounding suddenly very Poppins-ish. "A lot of my life happened in great, wonderful bursts of good fortune, and then I would race to be worthy of it." There must, surely, have been temptations along the way.

"Well," she says, "I can't drink too much without getting absolutely silly. And drugs have, mercifully, never worked, so I think I'm far more frightened of being out of control." What drugs did she try? "I didn't! Really, I didn't! I don't know why." She giggles.

After The Boyfriend Andrews had another successful run in the stage production of My Fair Lady, but it was Mary Poppins, for which she won an Oscar, that made her name. A year later, in 1965, she starred in The Sound Of Music, and her fortune was sealed.

Since then, of course, the film has had a life of its own. I ask why she thinks she is a gay icon. "I don't know. I'm sort of aware that I am. But I'm that odd mixture of, on the one hand, being a gay icon and, on the other hand, having grandmas and parents being grateful I'm around to be a babysitter for their kids. And I've never been able to figure out what makes a gay icon, because there are many different kinds. I don't think I have the image that say, Judy Garland has, or Bette Davis." I suggest these women encouraged their camp status by taking sidelong looks at the world. "I bet they weren't," says Andrews, as if the very suggestion of irony is insulting. "But I don't know whether longevity has something to do with it. I honest to God don't know. It's very flattering, in a way."

As well as Emma, Andrews has two daughters with her second husband, Blake Edwards, director of the Pink Panther films. The couple adopted Amy and Joanna from Vietnam; they are now 29 and 30. "We didn't even think about what we were laying on them at the time," she says. "We only knew what we hoped to do for them. Anyway, they survived. But they are [ ready to visit the Far East] now, and they want to do it and I've said that we'll go."

Andrews's singing career is over, but the success of The Princess Diaries has revived her acting career, and she has other projects on the boil. With her daughter, Emma, she has written several books for children, which are published as the Julie Andrews Collection, an imprint of HarperCollins. The collection will be available in Ireland for the first time next year. And she is busy with her seven grandchildren, who are scattered, for the most part, near her home in Los Angeles.

There are two questions that remain unanswered. One: was Christopher Plummer, as is widely assumed, playing Captain von Trapp for laughs? "I don't think so. We see quite a bit of each other, and" - she whispers - "I think he's quite pleased that he did the film." (He made a terrible fuss about it at the time.)

And Dick van Dyke: did she notice during filming how terrible his accent was? "Um. Yeah. And he did too. He's darling about it. Absolutely sweet. And he says: 'Ugh, I'm so terrible, but I tried.' It is what it is, and one wouldn't change it for anything. Fond memories." Does she think Mary Poppins and Bert ever got it together? Andrews gives a filthy laugh. "I hope so. She wouldn't admit it, but I do hope so."

The Princess Diaries 2: Royal Engagement is on general release