John Barrowman didn’t need a Tardis (Doctor Who’s famous spacecraft and time machine) to take him into space. All it took was the news that Captain Jack Harkness would be getting his own show and he was over the moon.

When viewers last saw Captain Jack in Doctor Who, he was stranded on a satellite many thousands of years in the future.  He had heroically faced down a Dalek invasion to protect his new friends, The Doctor and Rose – but his fate was unknown.

Now Jack is back, and in Russell T Davies’s dark and sexy sci-fi thriller the Time Agent from the 51st Century is at the helm of Torchwood, an elite, alien-fighting organization on the front line in the battle to protect the human race.

“Jack heads up a team of secret agents who are separate from the Government, outside police jurisdiction and beyond the United Nations. At Torchwood, they answer to no one but themselves.  They make their own rules,” explains John Barrowman, who plays the enigmatic action man with the mysterious past.

“Jack’s the leader and the glue – he keeps everyone together.  He’s the hero … although I don’t think he’d call himself a hero, he’d just call himself a man who does the job because it needs doing.”

But, says the actor, the journey from his terrifying Dalek encounter to 21st-Century Cardiff – home of the hub, Torchwood’s top-secret HQ – has left its mark on Jack. “Jack’s a little bit darker and he’s a little bit angrier than when we last saw him. After all, he was ditched on that satellite and who wouldn’t be angry about that?” he says.

“Towards the end of Doctor Who, Jack was becoming more human – I mean human in the sense that he was starting to feel for other people rather than just thinking about himself.  As Torchwood begins, he’s lost some of that. He doesn’t always consider other people’s feelings – his priority is the good of the world.”

Some things, however, never change. “He’s still fun, he still has his dry sense of humor and I think he’s still sexy,” says the actor, revealing that Jack is back to his old tricks, putting his moves on everyone and, well, everything. “It doesn’t have to have a pulse for Jack to fancy it. And if it’s got a zip code, he’ll sleep with it,” he quips.

For John (38), making Torchwood has been a huge thrill. “When Russell T Davies and Julie Gardner and I first sat down to talk about giving Captain Jack his own series, I was completely bowled over. It was a childhood dream to be a character in Doctor Who, so to have my own series was just unimaginable.

“I’m a grown man who gets to go to work every day and fight aliens, play with guns and kiss beautiful people – what more could I ask for?”

Born in Glasgow , John moved to Joliet , Illinois , with his family when he was eight years old.  At high school, he starred in an end-of-term musical and never looked back.  On a visit to the UK in 1989, he chanced upon an open audition for a West End production of Anything Goes and, after wowing leading lady Elaine Paige, was plucked from obscurity to star in the Cole Porter classic.  Acclaimed roles in a string of hit musicals followed, including Miss Saigon, Phantom Of The Opera, Sunset Boulevard and Beauty And The Beast.

The actor has also appeared in the BBC kids’ show Live And Kicking, the 2004 film De-Lovely, celebrity reality show Dancing On Ice and, most recently, as a judge on the BBC series How Do You Solve A Problem Like Maria?, the search for a new London West End star for The Sound of Music.

A life-long fan of Doctor Who, John admits that his home is stuffed with Captain Jack memorabilia, including his racy leather trousers, squareness gun and the bullets he aimed at the Daleks when we last saw him.

“Jack’s not a time traveler, he’s a Time Agent and he can only travel through time with the assistance of someone like The Doctor.  Now, Cardiff has this rift in it and so it’s one of the places the Tardis is likely to return to, so Jack is just waiting. He never leaves, he never sleeps,” says John.

It can be a lonely existence but Jack does find someone to confide in. “Jack gets on with everyone in Torchwood but the only person who knows anything about him is Gwen. Gwen comes in and she brings something new to the team – she brings heart. And, for some reason, Jack starts to reveal things to her.”

But even Gwen and Jack have their disagreements, he admits. “Every now and then there are major in-house battles. There are always tensions bubbling away because they’re facing life-or-death situations every day. Sometimes Jack gets very angry because the team doesn’t understand why he’s doing what he’s doing. But Jack has seen Earth’s future and he knows that the 21st Century is when it all changes – and they’ve got to be ready.”

Cardiff ’s space-time rift is the key, reveals John, because it acts as a gateway to Earth for a bone-chilling procession of aliens, including the Weevils, a race of wolf-like creatures that live in the city’s sewers.  “The Weevils are one freaky bunch of aliens,” he chuckles. “And every once in a while a Weevil goes rogue and attacks.  That’s when we have to step in because they can be mighty vicious.”

Sewer-dwelling aliens aside, John loves working in Cardiff and has even bought a house overlooking the bay, which he shares with his partner, architect Scott Gill, and their two cocker spaniels, Penny and Lewis. “When you see Cardiff on film, it looks like LA; it looks amazing,” he says. “I’ve seen the first episode and Cardiff surprised even me. I think a lot of people are going to want to come here, not just because of Torchwood but because it’s such a great place – it’s buzzing every single day and it’s beautiful.”

John is hoping to find the time to give his family a guided tour of the state-of-the art BBC studio complex where Torchwood is filmed. “It’s a great place to work,” says John. “Doctor Who is filmed there, too, and the Tardis and the Hub are right next to each other – the only thing that separates us is a curtain. We all arrive at work and go off to our separate areas and then we have a big shared lunch place. So you might sit down with your salad next to a Weevil or share a pizza with a Dalek … that’s pretty normal for us,” he laughs.

But not everyone shares the actor’s enthusiasm for the BBC canteen. In fact, it was all a bit much for one little boy, the son of one of the Torchwood crew, who recently accompanied his dad to work.

John explains: “We were having lunch and suddenly this very recognizable alien walked by and the child just freaked out. He screamed and his dad grabbed his hand and said, ‘You’ll be fine – you’re with me’. But the kid shouted: ‘No! You can’t do anything – I have to be with Jack!’ He literally ran over, grabbed onto my leg and wouldn’t let go. And the poor old alien was only going outside to have a cup of coffee and a cigarette!”