The Brit who plays the suspect U.S. hero

On TV, he's a certified American military hero, first as Army Maj. Dick Winters, the central character in HBO's epic 2001 mini-series,

Band of Brothers

, now as Marine Sgt. Nick Brody in Showtime's riveting

Homeland

.

Off camera, he's a Londoner of Welsh extraction, an Eton grad and Royal Shakespeare Company trouper.

There are times when even he gets confused.

"On the weekends, I'll wake up, go to the store, do some errands and realize, 'I've been talking like an American all day,' " Damian Lewis, 40, says by phone from L.A., where he's shooting the eighth episode of Homeland.

Curiously, it's the weather that causes him to toggle between his true self and his adopted persona.

"When it's cool at home, I'm Celsius. I go, 'Oh, my God, what is it, like 8 degrees outside?' When it's hot, I go Farenheit. Then it's, 'It must be 85 degrees out there!' "

He hadn't realized that he was playing a serviceman on cable for a second time until it was pointed out to him.

"That's superficial to me," he says. "They're such radically different people in radically different circumstances. In terms of military bearing, yes, I find similarities. For a dithering actor like myself being able to play military men who are trained to make decisions quickly and act on them decisively is very therapeutic."

To play a tortured POW like Homeland's Brody takes some commitment.

"I lost a lot of weight for this," Lewis says. "I wanted to be skinny. I'm not the most buff dude on the block, but I thought for truthfulness, this man has been in a hole for eight years. It would be ridiculous for him to take off a shirt and see a gym body."

He also did extensive research on post-traumatic stress disorder.

"So many guys come back with an inability to have a tender, loving relationship with their wives. And sometimes an inability to love their kids," he says. "They look forward to seeing them and then they're shocked and confused by their own lack of interest.

"And that's just from a 12-month tour of duty, from being engaged in live fire in that rough, all-male setting. Imagine being a POW for eight years and being brutalized that whole time.

"Brody is treated as a war hero but he's carrying a massive secret," continues Lewis. "Carrie Mathison [Claire Danes] is convinced he's not everything he appears to be."

Speaking of pretenders, how does a Brit end up getting handpicked by Steven Spielberg and Tom Hanks to play a WWII hero from tiny Ephrata in Lancaster County?

"Steven and Tom didn't know me from Adam," he says of the massive cattle call for Band of Brothers. "I was just an up-and-coming actor. Not even a star in England. I went through the standard selection process. Then they kept calling me back for interview after interview."

Lewis used what he calls "a generic American accent" during the auditions, then worked with a dialect coach once he was cast.

He wasn't the only guy on the Band of Brothers set affecting an accent.

"It was hilarious," Lewis says. "You had actors from Brooklyn doing New Orleans accents and Englishmen like me playing Pennsylvania accents. It was a Tower of Babel. HBO sent a note [to the cast] saying: 'Lose the accents. It's too crazy.' "

At this point, Lewis has portrayed Americans so often it's become second nature.

Sarah Shahi, who played his L.A.P.D. partner on the shamefully overlooked NBC series Life, says, "He is a rare combination of playful and professional. He has an ease and charm about him that is infectious. Working with him for two years was nothing less than a joy. And though his American is probably better than mine, I never forgot that he was British."

Lest we forget, before he became a replica Yank, Lewis was a distinguished stage actor in his native land.

We've been meaning to ask, Damian, is there a private club for thespians like yourself who have trod London boards as the melancholy Danish prince Hamlet?

"Yes, there is," he confides. "Dress code: tights. Password: codpiece."

There were a couple of things that lured him back to the States to star in Homeland.

"It's a phenomenal script, better than anything I'd been reading," he says. "It's in the thriller genre, but it's very ambitious. The plot goes to a more complex, nuanced place than you expect."

"We have a tough job with this material. It's rich and complex and could be played a lot of different ways," says Morena (V) Baccarin, who plays Brody's wife. "Damian being such a smart and giving actor makes a project like this go far more smoothly."

The other aspect of Homeland that Lewis liked is that it's cable, which means a far more condensed shooting schedule than for a network series.

That means more time at home in London with his wife and two young children. It also allows his spouse, Helen McCrory (Narcissa Malfoy in the Harry Potter films), to take on her own acting jobs.

"It's an ongoing discussion with my wife," he says. "You have to learn how to share your year."

At home, Lewis uses his adopted American enunciation only to amuse his son. Dropping into a charming British accent for the first time in the interview, he mimes the boy: "Oh, Daddy, stop it! Stop talking silly!"