It was his failure to get a Green Card that prompted Bernard Cornwell to write his first novel, but his historical thrillers have sold more than 20 million copies. He tells Nick Morrison how he got started - and what he makes of the TV adaptations of his Sharpe series.

BERNARD Cornwell had always felt a bond with Bamburgh Castle. On previous visits to Northumberland he had gazed on it in awe, but it was with something more than mere admiration. It was only after he met his natural father that he discovered the castle had once belonged to his ancestors.

"I had been on holiday there and I found I was drawn to it, and it was only later I discovered the connection," he says. "I found out we were directly descended from the guys who ruled Northumbria.

"They owned Bamburgh Castle, which wasn't a castle then, it was a wooden fort. Of course it was 1100 years ago."

His reunion with his father four years ago and the revelations over his ancestry provided inspiration for his new series of historical novels, a departure from the Napoleonic Wars-set Sharpe series.

The Last Kingdom, and his new book The Pale Horseman, take place during the Viking invasions. The hero of the series, Uhtred, who takes his name from Cornwell's ancestors, is forced to flee his family's Northumbrian estates and the books chronicle his split loyalties between the Danes and Alfred, the ruler of the last Anglo-Saxon kingdom still holding out.

"One of the questions I had about my family was how the hell they survived. How come, when the Vikings invaded Northumberland, they managed to cling on?," he says.

"Part of the reason was they had a terrific fortress, and probably they collaborated as well, but my preferred answer is that they were heroic. At least they survived up until that late 11th century, when they got turfed out just before the Norman Conquest."

He was born in 1944, the result of a fling between a member of the Woman's Auxiliary Air Force and a Canadian airman, and adopted by a couple who were members of a puritanical religious sect. The Peculiar People followed a literal interpretation of the King James Bible and he says his fascination with the military was in part a reaction against their pacifism.

"I was interested in everything they hated. They hated alcohol, tobacco, blondes. They were fundamentalist Christians, original members of the fun prevention league, and I reacted against them.

"They're all dead now but there was never any great love lost. They were just the wrong people to adopt anybody. It was horrible for them and not very nice for me," he says.

Cornwell, who returns to the North-East tomorrow to sign copies of his latest book, only turned to writing when he was unable to get a Green Card. After a stint as a teacher he became a journalist, ending up as head of current affairs for the BBC in Northern Ireland. It was in Belfast that he met and fell in love with Judy, an American.

With Judy unable to move to Britain for family reasons, Cornwell and his new wife went to the United States. Refused a work permit, at the age of 36 Cornwell turned to writing.

"It was a stupid thing to do, but it worked," he says. "You give up your career, go 3,000 miles to a place where you can't get a work permit and promise this lady you will earn a living writing a book. I was terribly lucky."

He had always wanted to write, but says he wasn't sure he would have had the courage if he hadn't been compelled by circumstances. But there was never any doubt about the subject of his books.

"When you start to write, you write what you want to read. As a kid I loved Hornblower, and when he stopped I wanted more. Actually, what I wanted to read was stories of Wellington's army, and there were none available.

"I was an anorak on the subject, I was very boring on it right from when I was a teenager. I knew quite a lot, although I didn't know I would end up writing about it," he says.

His initial approach was extraordinarily methodical, and a lesson for any would-be writers who sit at a desk waiting for inspiration. He chose books he liked, found out how they were put together, and then copied their structure.

"It worked perfectly. I never know why other people don't do it," he says. "If you decided you want to make the best mousetrap in the world, the first thing you do is get all the other mousetraps and find out how they work.

"I got hold of three or four best-selling books I liked and literally broke them down paragraph by paragraph, into where there was romance, where there was action, where there were flashbacks. I ended up with these charts coloured blue and red.

"Maybe it was instinctive anyway, but when you are starting there are certain things you don't know how to do. I talk to a lot of people who are writing their first books and the question they often have is how do they move a scene on, and that is where the charts helped. Certainly, after the second book I never used them again."

His Sharpe series now runs to 20 novels, with many of them filmed for television starring Sean Bean. Although he admits Bean did not fit his picture of Sharpe, now he finds it hard to think of his hero without hearing Bean. But he's not precious about the liberties taken with his work to make it suitable for television.

"I think they're wonderful. I have no problems with them whatsoever. I take the view that if I start making objections all I'm doing is putting obstacles in the way of people who want to give me two hours free advertising on television.

"I hear Sean now when I write Sharpe. There must have been a dozen books before Sean came along, and in my eye I still see the Sharpe I always see, but I hear Sean," he says.

While his books are best-sellers, he says he's uninterested in critical acclaim, and quite happy for his work to be labelled under historical fiction rather than literary novels.

"I like what I do. I'm a story-teller, an entertainer. Why would I want to do anything else? So a couple of London critics can say how awful I am? It would be a daft thing for me to do. I don't think anybody opens a Bernard Cornwell wanting a story about the human soul," he says.

Although they might be 1,000 years apart, his leap from the Napoleonic era to Anglo-Saxon times came easily.

"It is a story I have always wanted to write. It is an incredible story, in a sense the story of England. Before this, there was no such thing as England, after it there is.

"At one point, a point in The Pale Horseman, the whole thing almost ceases to exist and if things had turned out differently we would be living in Dane Law now and we would be talking Danish. Although we would also be having guilt-free sex," he says.

His books are littered with battle scenes, but he says writing about violence never tires him. "I should probably go and see a psychiatrist," he says. But the battles do come in handy. "I wouldn't say it's the most enjoyable bit to write, but in some ways it is the easiest because I have been doing it for so long now. It's also terrifically good to mop up the plot."

* The Pale Horseman by Bernard Cornwell (HarperCollins, £17.99). The author will be signing copies at Ottakars in Sunderland tomorrow from 12.30-1.30pm, then at Waterstone's, Emerson Chambers, Newcastle, 3-3.45pm.