Just another day in the life of Torchwood's Gwen Cooper.

During the first two series of the Doctor Who spin-off, ex-police officer Gwen has been the mainstay of the Torchwood team - the mother of the group who calms the others, in comparison to flamboyant team leader Captain Jack Harkness.

In the forthcoming five-part series, which will be shown on consecutive nights from Monday July 6, her role is developed even more.

Eve Myles, the actress who plays Gwen, explains that the new series is where she really comes into her own.

"From episode two onwards, Gwen has the responsibility of the world on her shoulders. It just doesn't let up until the final scene and it's life and death every minute of the day," she says.

"I absolutely love playing Gwen. She's constantly evolving and, in this five-parter in particular, there's not time to have second thoughts. It's always Plan A, because there's no time for a plan B, C or D.

"I was in agony playing her this time around. She's still very real and earthy, and knows more than ever she could be taken out just like that."

She explains that in the new series it's clear that all the characters feel fragile.

"Tosh or Owen (characters played by Naoko Mori and Burn Gorman respectively, killed in the last episode of series two) act as great symbols of how quickly you can be taken out of Torchwood."

The latest series, Children Of Earth, starts with reports flooding in of freak paranormal activity.

The newly-depleted Torchwood crew spring into action, determined to find out what could have caused every child on earth to turn and face in the same direction and repeat a spine-tingling chant.

They begin by establishing links and following up on leads, getting closer to the truth. But the team have no idea that the Government has turned against them and want to shut down their alien-hunting unit.

Since its start in 2006, Torchwood has been praised for the way it mixes science fiction with domestic drama. In one 10-minute section, you can have big fights with an alien one moment and a romantic scene the next.

Children Of Earth is no different, with the relationship between John Barrowman's Captain Jack and Ianto, played by Gareth David-Lloyd, becoming much more serious.

Gwen also has her own personal issues to deal with. "It was great when I first read the script," says Myles. "Not only is she going to save the world, she's also going to be a mummy. I think that highlights her dedication to Torchwood. She's still Gwen Cooper, the girl-next-door you met three years ago, but she's developed massively and she's going to be a mum now.

"I can't wait for the next series. I can imagine her saving the world and then going home to the family. It gives her a new dimension, and a very strong motherly dimension. She's the mother of the team already, and a fighter, and a mother away from them too. To play those two sides is really exciting."

In a case of life imitating art, 31-year-old Myles is pregnant too. "Yeah, so there's a bit of news for you," she beams. "I'm due in November. It's been killing me keeping it to myself but now I'm telling everyone!

"It was funny because John (Barrowman) knew something was up and he was texting and ringing me all the time but I couldn't get back to him. Then he'd say, 'How are things?' all the time, knowing something was up. It was great to be able to tell everyone. I'm over the moon.

"I'm going for a swim in his pool over the summer," she continues. "He keeps saying he's going to sell tickets at Sea World! He's definitely going to be a guncle, that's a new word I've just heard for gay uncle!

"I wasn't pregnant when we were filming Children Of Earth, but I am doing something at the moment and they've been brilliant - big bags, scarves, things like that to cover me up. You can see the bump normally, but the character has been wearing these big floaty dresses so it's great."

With Myles in confessional mood, you'd think it might be a good time to squeeze some Torchwood-related secrets out of her, but professional as all Doctor Who and Torchwood actors are, no hidden treasures are forthcoming.

"I can tell you a bit about the 456," she offers. "You're going to see it in Children Of Earth. It's the biggest threat that's ever come to earth and it's absolutely disgusting. It's been built, the guys did an amazing job on it.

"This isn't me hiding from the question, but as horrible as the 456 is, you'll learn from watching this that humans are the biggest monsters of all. There's a lot to really look forward to."

Extra time - Eve Myles

Eve was born in Ystradgynlais, South Wales.

She trained to be an actress at the Royal Welsh College Of Music And Drama in Cardiff.

Her first major role was in BBC Wales's acclaimed series Belonging, in which she played Ceri.

She has worked with the Royal Shakespeare Company in Stratford, and in 2005 appeared opposite Michael Gambon in Henry IV Part I and II at London's National Theatre.

She lives in Cardiff with long-term partner and fellow actor Bradley Freegard.

Torchwood: Children Of Earth begins on tonight on BBC One and continues on consecutive nights for the rest of the week