I go to work every day and save the world.

You'd be forgiven for thinking John Barrowman has had a charmed life. But the boy growing up in America's Midwest with a Scottish accent and the knowledge that he was gay has had his fair share of struggles.

MINUTES into the interview with actor and musical star John Barrowman, just as a few question marks about him are forming in my mind, something very charming happens. A man hovers at Barrowman's back. Sorry to interrupt. Could his wee boy say hello? Certainly. The little boy, an angelic blond, is about three. He stares at Barrowman with the kind of look children often reserve for shop Santas: a mixture of rapt wonder and awe, tinged with a soupon of fear and disbelief. Speech has deserted him. This is Captain Jack from Doctor Who and Torchwood!

"I fight Daleks, Cybermen and travel round the planets with the Doctor," Barrowman tells his wide-eyed admirer with absolute conviction. What, says the father, did the little boy say he would do if he met Captain Jack? His son hesitates but Barrowman simply crouches down, opens out his arms to him and in a rush, the little boy wraps himself round him. "Oh, thank you," says Barrowman, "that's much better than fighting aliens." Captain Jack is such a hero that the boy even has a doll of him. "Ah," says Barrowman, "but you've seen the real guy now. That's me!"

It's not often in our society that gay men are allowed to be fantasy heroes to small boys. Captain Jack is a bisexual time traveller fighting to save the planet, and in real life Barrowman is gay too. He's in a 14-year relationship with Scott Gill, an architect. It's always a bit poignant watching gay men with kids, particularly when, like Barrowman, they have made no secret of the fact they would like to be a father. What appeals to him about fatherhood? "I don't know. I just think I would be a good dad. Scott and I have an incredible amount to offer a child. Gay men have two individual incomes and don't spend their money on anything but themselves, so we have money we could offer for a good education to help a child who didn't have anything, who grew up in an orphanage."

Would he be more interested, then, in helping an orphan than having a blood child? "I think it probably would interest me more but the side of me that is selfish would also like to have a blood child. If we were doing that we'd have one and adopt one. We also said we'd mix the sperm so we didn't know who was the father." He and Scott might prefer that – but would a child? Legislation now emphasises children's rights to know their origins. "Well, if they needed to, but I really think a child growing up in a loving home wouldn't care."

The home might be loving. The rest of the world isn't always. But Barrowman says the prospect of a child with two fathers being ostracised or bullied isn't a major concern. "You pack up and you move to a place where they don't," he says stoutly. Does such a place actually exist? But you'll always be picked on for something as a child, he argues. And he would give short shrift to the idea that, since a child is not the natural consequence of a same-sex relationship, homosexuals have no particular right to be parents. "These children are wanted. Think how much planning it actually takes. More planning than some people who just go out and get knocked up and have a baby."

So how would he and Scott plan it? Well, he did have a female friend who offered to be a surrogate some years ago. "I also have another friend now and she has said if I wanted to, she would."

Barrowman has an autobiography out in the next few weeks, written with his sister, a university professor in America. "You'll find out who this famous person is who would have the baby," he grins. (We'll also find out how a famous designer "tried it on in every way, shape and form".) His sister went everywhere with him for three months to write the book. "It was only sleep time and bathroom times she wasn't there – and even then she was sometimes shouting questions through the bathroom door."

He didn't find it hard being frank with his sister about his life and his sexuality? Not at all. And it gave her a new understanding of his life. "My sister said to me, 'I've now got a gay man living in my head.' I said, 'You should think yourself lucky, Carol. You'll probably dress more fabulously and have a bit more style!'"

AND THE QUESTION mark that had been forming? Perhaps it was to do with authenticity. Barrowman's voice is loud and declamatory and at first you feel as though you're in an audience (somewhere up in the gods). And there is something disconcerting about someone who switches from an American accent to a Scottish one, depending on who he is talking to, the way Barrowman does. At first, I just don't buy it. Rousseau wrote that accent "is the soul of talk; it gives it feeling and veracity" and most of us would instinctively agree. How many souls can a man have with any veracity?

But after a while, the question mark begins to fade. Barrowman is assertive and energetic and driven, and interviewing him feels a bit like violently shaking up a can of cola then opening it and letting the contents froth all over the place. But there's a kind of honesty and decency that emerges in the hubbub of his conversation. You start off wondering if he's a bit affected and end up deciding how genuine he is. "They are both real," he says when asked about his two accents. But which does he have to think about? "I don't have to think about either of them. That's the really strange thing and people don't understand it."

In Barrowman's case, I think the explanation is perhaps straightforward. It's not that he's trying to assume an identity; he's reluctant to lose one. "Maybe part of the reason I switch it on and off, and have the ability to do that, is because as a young person growing up I didn't want to lose my Scottish accent," he agrees. The two accents represent two parts of him. At the age of eight, his father's job prompted a move from Mount Vernon in Glasgow to the American Midwest. His elder brother had been accepted for the junior Rangers football team. His elder sister was set for university. So for them, the move was much more of a wrench. Barrowman was just excited.

Once there, he found himself teased about being Scottish so his shift to an American accent was pragmatic. Emotionally, he never forgot where he came from: the days of going to the record shop in Shettleston where his mum worked and singing on the counter after school; the hours spent in the high flats where his gran lived; vivid memories of the prefabricated housing of post-war Britain. In America, his life was "pretty much upper-middle class. A very comfortable atmosphere with big houses and nice cars, but we were always reminded that you get nothing for free. I was dragged out of bed every weekend to do the gardening. Hated it. When I went to university, my dad got a gardener. I said, 'Why are you getting a gardener?' He said, 'Because I can afford it.' And I said, 'Well. why didn't you get one when I was there?' And he said, 'Because we had you.'"

His mother was a fantastic singer. "She would have loved to do what I do but she grew up in the war and it was more important to have an Anderson shelter than go to a drama or music school." Barrowman inherited her musical talent. His late Aunt Dorothy used to phone him up and get him to sing down the phone to the girls in her office.

He has the super confidence of America, and the down-to-earth quality of Scotland. But ask him which facets of his personality he thinks have been shaped by each country and he says he's not sure, both societies foster an ambitious nature. His father, his uncle, his brother – all rose to senior positions in their jobs and he is aware of coming from a very close, very dynamic family. "Scottish people to me… I don't want to use the word 'aggressive' but they're go-getters. They're determined and they don't like to be told no. It's the same with Americans. Every time I come back to Scotland, there's always progressive change and that can only be from a society or culture that produces that kind of drive and ambition."

Barrowman studied at a university of performing arts but came to Britain on a visit in the late 1980s, auditioned for a role, and stayed. He quickly established himself as a leading West End man, with roles in Phantom, Chicago, Sunset Boulevard and Miss Saigon. He now has two homes in America, one in London, and one in Cardiff where Torchwood is filmed. But as an adult, he finds it easier to live in Britain and says he wouldn't go back to live full-time in the States. In Britain, we sometimes make the mistake of thinking America is one vast New York, but great swathes of it are dominated by social conservatism and fundamentalist Christianity. It can be hard to be gay there. "The British people are far more accepting of someone like me, whereas in America I feel they're going backwards with the human race. I find it terribly repressed and a lot of gay men pretend to be straight. It's only in specific cities that you get the openness."

He knew he was gay from an early age. There was no angst. "I remember it vividly. I woke up one morning when I was nine years old. I looked at a magazine and there was a man and a woman in it, and I looked at the man and got an erection. That's all I can remember. I was being taught by society around me that wasn't right." So didn't it frighten him to be consciously different at such a young age? "No. I don't know if it was because I had such a great family. I just thought, that's a bit different. I won't tell anybody. I had a great growing up with male and female friends. I dated girls because that's what everyone else did when I actually wanted to go to dances with my best mates. But I had been made fun of because of my accent as a child so I wasn't going to let that happen to me. I figured the best way to protect myself was just not to talk about it."

Did he deny it to himself? "No, I never denied it. Absolutely never denied it. I just had to do what I had to do until I went to university or college. I lived in a small town in the Midwest, but if you go to a bigger city people think differently and that's what I thought would happen." Perhaps not surprisingly, politically he rejects the right wing. "George Bush is a f***ing arsehole," he says, giving a little hint that the Glasgow boy is alive and well inside his American wrapping.

Barrowman and his parents were churchgoers – he retains a faith in God – but he refuses to accept fundamentalist views. "I just ignored what was being taught in the pulpit when I was going to church, that gay was bad. I just thought, 'I'm not going to listen to it, because I know I'm not a bad person.' I just always kept that in my head. I'm pretty generous. I'm pretty kind to people. I look after my family, my friends, and I will fight tooth and nail anyone who says I'm evil or bad. I believe I was made this way. If God can make so many different animals and so many different types of human being, with different skin colour and hair colour and eyes, why can't he make gay people?"

He gets letters from young men and women struggling with their sexuality and enjoys being a positive role model. But as far as Captain Jack is concerned, he doesn't really care about the character's bisexuality. "It's usually the press that make the issue about sexuality. The audience don't care," he says. Though he did get a letter from a mother in conservative North Carolina recently who said how lovely it was to watch an episode with her 14-year-old gay son and see a relationship between two men depicted that wasn't seedy or dirty.

Barrowman's own parents have always supported him. They have been married for more that 50 years and, actually, Barrowman has shown the same instinct for a steady relationship. He and Scott have a civil partnership. Coming out was not traumatic for him, but he understands it is for some people. "The thing that scares gay people, that makes them cry, is the possibility their family will shun them, that the people they love will say, 'We don't want anything to do with you any more.' And that's because society has given them a preconceived image of gay men which is that we're all effeminate or that we wear leather gear with your arse hanging out and you have sex in bad, dirty places. You don't do it like everybody else."

Barrowman is very direct in conversation. He fixes me with a look. "But I don't care who you are or what walk of life you're in. You probably do something that is slightly kinky in your bedroom. You just don't tell anybody." The eyebrows arch. "Am I right?" Mine arch back.

As he points out, homosexuality is often seen as promiscuous and seedy. So I wonder if Barrowman thinks the nature of homosexual love is any different to heterosexual love. "I go to bed with Scott every night and I probably have sex a little differently from a man and a woman, but I probably do the same kind of things a woman does to her husband, to be blunt. It's all very relevant and the same. Scott and I have had bumps in our relationship but I love him enough to look past those bumps to the greater picture. I think people give up too quickly on relationships. You know, it's not just about affairs. I'm talking about 'they get on my nerves because they leave the room messy all the time'. Well, pick it up. Sit them down and talk to them. Don't start getting aggressive. Scott and I do argue. It's healthy. But at the end of the night, one of us will always resolve it."

So what does love mean to him? "Companionship. Security – as in another person, I don't mean financial. Someone who will listen to you, respect you, do anything for you." But that doesn't come automatically. "You have to make an effort. My mum used to joke, 'You've got to do things to keep the spark alive.' And I said, 'Mother, I'm so glad to hear that! And I hope you and Dad keep the spark alive for a long, long time.'" He grins. "I've seen their wardrobe. I know what she's talking about. Let's just say dressing up occurs every so often. And you know what? That's what makes it work. That's why they've been together 53 years. That's what a relationship is about and it doesn't matter if you're two men, two women, or a man and a woman. It's actually very similar."

Never mind the Daleks, it's Barrowman who is taking over the universe. His success first came on the West End stage but television has made him a household name. It's not only Torchwood and Doctor Who. He pops up everywhere: on chat shows, discussion and political programmes, religious programmes, quiz programmes… In March he will even present a new children's series, The Kids Are All Right. He's been a judge on the BBC's reality shows Any Dream Will Do and How Do You Solve a Problem Like Maria? and competed on ITV's Dancing on Ice. Has he pencilled his nervous breakdown into the schedule? No, he'll have a breakdown if he doesn't work.

Is such a wide array of projects a sign of insecurity? Does he fear if he turns things down he won't work? No, because he's booked up to 2009. But he does have insecurity. In the business they call you a triple threat if you can sing, dance and act. He thinks he's a great singer. (There's no false modesty with Barrowman.) And he thinks he can act. But dancing is his weak spot, which is partly why he made himself do Dancing on Ice. (Plus it was learning a skill, not just sitting in a celebrity house or eating witchetty grubs in the Australian jungle.)

In many ways Dancing on Ice was the show that revealed most about him. He was clearly ferociously competitive. Yes, he agrees, being voted off was awful. It's a long story but at the end of the day his technique was actually better than… He breaks off and grins. "Listen to me," he laughs. "People say to me, 'John, let it go…' Nah!"

He admits he's very driven. "I am not going to lie to you – I am very ambitious," he agrees. "But I think I am ambitious in a way that would never intentionally hurt or damage anybody. I know people who are ambitious and ruthless, and I am not ruthless. If I know something is going to hurt someone, I will do my damnedest to find a way of doing it that won't hurt them – or I just won't do it."

Barrowman is very professional and good at lots of things, though that perhaps gives him more versatility as a performer than depth and subtlety. The strange thing is that everything about him seems very easy and charmed, as if he's never had to struggle in his life. (Even success was instant.) But if you've been gay – particularly in small-town America – chances are you have struggled, so it must be his attitude rather than his lot in life.

"I am like everybody else. I sometimes wake up in the morning and don't want to get out of bed. I sometimes get a bit depressed. I get upset. I have situations with family. But I am very happy. I can deal with all those things. That's life." A hero's life. "I get up every day and go to work and save the world. I kill aliens and protect the planet. Could you ask for anything more?"

The new series of Torchwood begins on January 16 on BBC2 at 9pm; Anything Goes: the Autobiography (18.99 HB, 10.99 PB, Michael O'Mara Books) is published on January 24