Elizabeth Buchan, a former winner of Romantic Novel of the Year, is often approached by readers at book festivals who ask whether she's related to the late, great John Buchan, novelist, politician and author of The Thirty-Nine Steps.

She tells them: "I'm the bolted-on Buchan," explaining that the late author was her husband Benjamin's grandfather, so she is actually married to a Buchan but was never directly related to the famous author.

Like her 'bolted-on' relative, one of her own books, Revenge Of The Middle-Aged Woman, was adapted for screen in 2004, but in the form of a TV movie.

"It was made into a CBS prime time telly thing," she recalls. "Occasionally you can see it in the deep outer reaches of Channel 5 in the afternoons. They made a very good job of it. My one regret was that the scriptwriter was much wittier than I was, and I wish I'd thought of some of her jokes."

She wasn't asked to go to the US or visit the set while the series was being made, she recalls.

"Writers tend to be pond life when it comes to films and telly. Unless you're a really big honcho, you're unlikely to be invited to the premiere."

But it doesn't faze the bestselling author of prize-winning romantic novel Consider The Lily, and whose short stories have been broadcast on BBC Radio 4. She has also chaired a number of literary prizes and is a judge in this year's Costa Book Awards.

Today, we're meeting to discuss her latest novel, I Can't Begin To Tell You, a story set in Denmark and London in 1940, in which a British-born woman, Kay Eberstern, living on her husband Bror's country estate in Denmark, is lured by British Intelligence into a covert world of resistance and sabotage.

While Bror co-exists with the Nazi enemy to preserve the legacy of his family home, Kay refuses to do the same and is tasked with protecting an enigmatic SOE (Special Operations Executive) agent.

It's a story of bravery, broken loyalties and lies created as a result of the war, but there's also tenderness and romance, played out urgently by couples who simply don't know if they will survive the conflict.

"If you read some of the agents' autobiographies, it seems that sex and love affairs was a way of affirming they were still alive. At the end of a day or night of hideous happenings, if you had another body next to yours, it made it possible. It wasn't necessarily to do with fidelity, it was just re-affirming you were human, you were alive and you could cope."

While Buchan was born after the war, in 1948, her father was an army major who was frequently posted abroad. At the age of eight, her parents sent her to boarding school in Bath, while they went off to yet another posting, which was when she began to take comfort from books.

"I was left behind at the age of eight while they went off to Nigeria with my two [younger] sisters. I was very lonely and bewildered. My overwhelming impression would have been cold and hungry. So I took recourse in books. I spent my life with my nose in a book - that began it.

"During school holidays, I was looked after by a granny or relations. Then once a year I was flown to Nigeria. It wasn't exactly normal, but it wasn't abnormal. But that separation for a child of eight is quite profound.

"They did it for the best reasons. I loved my parents, I'm not blaming them, but it set in motion a way of coping with the world which involved books. I don't want people to feel sorry for me, because I don't feel sorry for myself."

Buchan excelled at school and attained a double degree in English and history at the University of Kent, before clinching her first job as a blurb writer for Penguin.

"There was an office of four, run by a maverick genius, who said, 'Right, we're paying you to read through these books and then you write a fantastic blurb on the back so people will buy them'. I thought I'd died and gone to heaven."

Soon after, she married publisher Benjamin Buchan, after they met through a publishing friend. She knew as soon as she saw him that he was the man for her.

"This vision in a shabby navy blue overcoat got to his feet and I thought, 'That's it!' Well, he was the grandson of John Buchan who wrote The Thirty-Nine Steps, so I was pulled into that orbit at once.

"I didn't think the name would help me get on, because I can't claim it. I have to be very careful. I always say, 'I'm a bolted-on Buchan'. I just absorb the ambience."

While still at Penguin, she had two children, Adam and Eleanor, but also started writing books.

"I used to get up at dawn and do a page, then feed the children and go to work, on the assumption that a page would turn into two and then into four, and so it did. It must have taken me two to three years to write my first book (Daughters Of The Storm) about the French revolution, which was pretty dreadful. But I've re-written it recently and put it up on eBooks."

She never set out to write romantic fiction, she says, but was delighted when Consider The Lily won Romantic Novelist of the Year in 1994.

"I like literary prizes. I think they stir up conversation and possibly controversy, and if it makes people read them then it's great."

She herself is one of the judges of the Costa Book Awards and is reading around 50 titles.

"I'm reading all sorts of books that I never would have read, some of which have been a complete surprise and delight. It brings it to the attention of the public."

An avid Twitter user, she laughs when asked if she is easily distracted by the internet when writing her stories.

"There's a wonderful app which I'm thinking of buying, where you tell it to shut down your internet for hours at a time and it does it. The temptation to wander the byways of Facebook and Twitter is enormous."

For now, she's concentrating on her next book, Aftermath, which is about a German bride coming back into an English family after the Second World War.

Buchan writes from her London home, but she doesn't churn them out - one book around every 18 months to two years is her norm.

"There's a great danger of being pushed by publishers who say, 'We want another one, we want another one'," she says. "But if you are to try and make your books as good as you can, you must have thinking time and doing time."

:: I Can't Begin To Tell You by Elizabeth Buchan is published by Penguin/Michael Joseph on August 28, priced £14.99