THE chance to do some dangerous undercover work in the first of three new Foyle's War on ITV really appealed to Honeysuckle Weeks, who plays Samantha Stewart and has a secret of her own in the post-war thrillers penned by Anthony Horowitz, which will be shown early next year.

“It’s really exciting as Sam runs into danger. We’ve filmed scenes where her life is under threat at gunpoint," says Weeks, who has evolved with the popular series from police driver to espionage expert.

“I wish I hadn’t previously met the actor who is playing the man chasing me because he’s extremely nice – and it’s very hard to be frightened of someone who is so nice,” she says.

Weeks takes on a new identity to became the live-in companion of retired Texas oil tycoon Andrew Del Mar, played by Frasier star John Mahoney.

“The job is basically reading to an elderly gentleman but she doesn’t realise just how sinister her employers are. She is not aware of the possible dangers that may lurk in this enormous and mysterious household. Sam says to herself, ‘Well how dangerous can it be? It’s just an old gentleman and all I’m doing is reading and taking a quick snoop in the study'. But it turns out these are very powerful and dangerous men who you really do not want to cross. I was a huge Frasier fan and of John's character Martin Crane. John is hilarious. He’s got so many fascinating anecdotes,” says Weeks.

Sam is the trusted associate of Christopher Foyle (Michael Kitchen) in his 1946 role as a Senior Intelligence Officer for secret service MI5. The secret Sam is keeping from Foyle, when she and politician husband Adam (Daniel Weyman) have moved into a new house, is that she is three months pregnant with their first child.

“Foyle doesn’t know that Sam is pregnant. And if he did know, I don’t think he would have let her take the undercover job on. In fact, no pregnant woman would ever put herself in that position. Certainly if Sam had known that’s how things would turn out, she wouldn’t.

“She’s a bit of a modern woman for that era. When women got married in those days they had babies and that was it. MI5 did let pregnant women still serve and work, but once they had the child they would have to leave. So she fears she is about to lose all her independence and the life she has. Women had seen another world during the Second World War when they took on jobs men had previously done and, for some traditional roles were no longer seen as enough."

At the outset of episode one of this ninth series, Sam tells her husband about working with Foyle, saying, “You have no idea how much we’ve been through together.”

Weeks says: “As often it is in life, perhaps one’s partner might not necessarily be the person who knows one best. Foyle is rather like a father figure to Sam and has seen her grow up. He took her on as a very jolly hockey sticks ingénue, slightly daft but enthusiastic and well meaning young girl. Who was, frankly, a bit incompetent.

“And as the series has gone on the writer Anthony Horowitz has evolved the character as she would have naturally developed.

“Now she’s not going to make as many errors and understands a bit more about the politics. She’s not completely clueless as she was in the beginning. Sam has been in some scrapes and been saved by Foyle. They have a complicit understanding of each other and she treasures that. But it’s now put in jeopardy by this pregnancy.

Weeks was 21 when she filmed the pilot episode for Foyle's War and is now married with a child.

"I’ve grown up with the series. When you’ve done a show that has been as successful as this for as long as it has been, it is a joy to return to filming. It’s like a family. Anthony writes brilliantly for me and I love the character.”

She describes leading man Michael Kitchen as “a bit of a dark horse”.

“I know everyone is so curious about him but he likes to keep his mystique. He feels if people knew who he was they wouldn’t believe him playing his parts. But I just think he’s shy. He is also a brilliant pianist and great musician. And he got me front row tickets to see the Rolling Stones at Wembley. Which was really cool.

“In terms of the character, I think Foyle needs a woman in his life. It’s high time. His wife died at least ten years ago and he deserves a bit of companionship.”

Weeks studied at the Sylvia Young Theatre School and recently introduced a new face to their agency – her son, Wade, aged three.

“I have signed him up with my ex-agent Sylvia Young’s. He’s on the books. The only trouble is he likes to defy orders. Unlike me. I was always very obedient.”

Can she see mother and son acting together when he’s grown up? “Yes. Except he’d be embarrassed by me. I’d feel too self conscious because he’d be telling me I was rubbish. I can see it coming,” she laughs.

For now, she is simply concerned with ensuring Sam survives the ever present danger in Foyle’s War.

“There’s always been a lingering bomb, a spot of Anthrax, possible drowning or garrotings. You name it, the danger is there. People feel for Sam so I think Anthony likes to put the character in jeopardy. I’d miss her if they ever did kill her off. I believe these last few series are the best written and the most exciting we’ve ever made. I think the audience will love this new series. It’s a really proper thriller.”