As Citadel, the final book in her Languedoc trilogy, is published, bestselling author Kate Mosse talks about turning down Hollywood in favour of a British TV adaptation of her bestseller Labyrinth, and her joy at clinching a cameo role in the forthcoming mini-series. The author, whose epic adventures have been translated into 35 languages, reveals how she learned to shoot as part of her research for the latest book, which centres on an 18-year-old French resistance fighter.

By Hannah Stephenson

Standing on a hilltop in south-west France, addressing actors John Hurt and Vanessa Kirby, proved a surreal experience for best-selling novelist Kate Mosse.

The 51-year-old author of Labyrinth and Sepulchre, the first two in her blockbuster Languedoc trilogy, had clinched a cameo role as a tour guide at Montsegur in the forthcoming six-hour mini-series of Labyrinth.

"I have a few lines at the end," she says, smiling. "It's my first acting role and I'm comfortably sure it will be my last. The actors were both standing with me, looking at me as I was talking. It was an extraordinary sense of my characters coming to life."

In both Labyrinth and its sequel, Sepulchre, feisty female heroines lead the action. Citadel, the third in the Languedoc trilogy, also features stories from two eras, following the fortunes of heroine Sandrine Vidal, a young resistance fighter in Carcassonne and her network of women resistantes, codenamed Citadelle.

She becomes involved in the quest for an ancient codex containing secrets which could change the course of the war. But collaborators with ugly motives are also searching for this document. Interlinked with this tale is the story of a medieval monk smuggling a forbidden manuscript into the region to prevent its seizure by intolerant Christians.

Mosse was still writing Citadel when Labyrinth - which also stars Janet Suzman and Jessica Brown Findlay (of Downton Abbey fame) - was being filmed. Seeing John Hurt as a character who appears in both books had an influence on her writing, she reflects.

"It was very odd seeing a character that I'd invented in Labyrinth coming to life and then influencing how he subsequently appears on the page in Citadel. All the time I was writing Citadel I had John's voice in my mind."

The spirit of the book is bang on, she enthuses.

"I cried for the last hour and a half because they'd done it so well."

The series, which was executive produced by Ridley Scott and his late brother Tony, will air on Channel 4 next year. Mosse turned down the chance to make Labyrinth into a Hollywood movie before the TV deal was struck.

"When Labyrinth became a worldwide hit, we did have conversations with Hollywood but my agent and I didn't feel you could ever do it [justice] in a couple of hours.

"Everyone was talking about the male lead, but the leads are women. So we turned down Hollywood."

All three books are set in Carcassonne, a region of France which she holds dear. She and her husband Greg, a creative writing teacher, bought a house there in 1989. They used to spend half the year there with their two children, who are now grown up.

"So much of my writing of the last 23 years has been inspired by falling in love with the place. My husband had lived for some time in Paris. My mother-in-law was retiring and had a little bit of money so we just pooled resources and it seemed a lovely thing to do because we were teachers and writers and having somewhere to go is a lovely way of having a holiday every year. The minute I arrived, the place felt like home."

They spend less time there now because of work commitments, so it has become their holiday home.

As part of her research for Citadel, she learned how to fire weapons from the Second World War, receiving lessons at the Ministry of Defence training range at Shrivenham, near Swindon.

"I was shown all the Second World War pistols and sub-machine guns, rifles, the lot. It was the first time I'd ever held a gun, let alone fired one. I was a dreadful shot."

The eldest of three daughters of a solicitor and teacher, Mosse grew up in Chichester, West Sussex, and was penning stories and plays from an early age.

"Books were a part of everyday life, which is one of the reasons I'm so involved in the library campaign. Children who grow up thinking that books are a normal part of life are more likely to be successful in education. For me libraries are the absolute symbol of that."

An accomplished violinist and pianist, she won a place at music college, but at the last minute realised she was never going to be good enough to be a soloist, so went to Oxford University to read English.

After university, she worked as a secretary in a publishing company and was advised by an agent to write her own books.

Success was slow, though, and she wrote several non-fiction and fiction books before she hit the big time with Labyrinth in 2005. Since then, her books have sold in their millions in 40 countries.

Women are at the heart of her stories, which are essentially action adventures and as the Orange Prize founder, women's fiction is immensely important to her.

"I write adventure fiction, in the tradition of Jules Verne and Rider Haggard. People like stories of active men and women. A lot of teenagers, who have grown up with Hermione Granger and with computer games featuring male and female avatars, read my work."

Now that Orange has ended its sponsorship of the competition, the 2013 'Women's Prize for Fiction', as it has been renamed, will be funded by a range of companies and individuals, while the board is in talks with potential sponsors for 2014 and beyond. Mosse cannot emphasise enough the importance of such prizes.

"There's a lot of attention on commercial fiction but with literary fiction, the real issue is keeping books on the shelves for long enough to dig their heels in. Sometimes books don't find their audience straight away. That's why prizes matter a great deal. They buy those books which are exceptional more time in the sun."

A former prize-winner herself (she won the Richard & Judy Best Book at the British Book Awards in 2006), Mosse doesn't class herself as commercial or literary fiction.

"I have commercial sales but often I'm reviewed in a more literary way. I don't get too worried about the labels put on things."

Richard & Judy helped Labyrinth enormously, she agrees, although it was already a best-seller in hardback before the book was highlighted on the show.

"Being picked in paperback for Richard & Judy was enormously important. It was on the show in January, sold 55,000 copies the next day and stayed at number one for the next six months."

Her husband Greg, who took her name when they married, reads her drafts before they are submitted. They never row about his editing advice, she says.

"Because Greg is a writer and a teacher and an editor, it's different, but when people ask for my advice I'd say never give it to somebody who loves you because you will hate them if they're critical and won't believe them if they're nice."

Talks are currently taking place regarding TV adaptations of Sepulchre and Citadel, while Mosse has also been given the green light on an adaptation of her stand-alone novella, The Winter Ghosts.

For now, she'll bask in the glory of finishing her trilogy, is working on a number of plays and will be starting a novella next autumn.

She has never taken her success for granted and is still amazed at how well her books have sold.

"It's an extraordinary feeling. I've been published well, I've been lucky and I wrote the kind of book that readers wanted at the time they wanted it. You can't chase those trends."

:: Citadel by Kate Mosse is published by Orion, priced £18.99. Available now