Authors get a boost from screen

When HBO first announced plans to adapt George RR Martin's fantasy novels in 2007, there was, admittedly, a murmur of excitement. And interest in his A Song of Ice and Fire series built to such a degree that, by the time it premiered in April, it was already the most eagerly anticipated show of this year. But even Martin himself couldn't have expected what would happen next.

At the time of writing, A Game of Thrones - the first book in the series and the name by which HBO's drama is known - inhabits the number two slot in the UK Amazon charts, beaten only by the timely interest in Téa Obreht's Orange Prize-winner The Tiger's Wife. Staggeringly, three more are also in the top 10. In the US, it's much the same: the Thrones box-set, containing the first four books, is the only fiction entry in Amazon's bestsellers list. Canada and Germany have also been bitten by the Thrones bug. Not bad for a book first published a full 15 years ago, is it?

It would be wrong to suggest that the Song of Ice and Fire saga was unheard of before the much-hyped HBO adaptation. But the books were very much a cult concern - albeit a rather large cult which already had millions of members - before one of the creators of the television series, David Benioff, called it "The Sopranos in Middle Earth". At a stroke he grabbed the attention of both Tolkien and serious drama fans - a rather broad constituency. The series has clearly been good business for Martin and his publishers.

Of course, Martin isn't the first author to enjoy a welcome sales spike on the back of a popular television or film adaptation. Authors these days generally don't get too fussed about the editing of their finely honed opus into bite-sized scenes, because they know the fortune that can be accrued from the simple phrase "now a major motion picture" stamped across the front of their book. Chuck Palahniuk, for example, was the epitome of the struggling author before the David Fincher-directed adaptation of his 1996 novel, Fight Club. The re-released novel actually had the film's stars - Brad Pitt and Edward Norton - on the jacket, and the book sales went through the roof. Palahniuk has even gone on record to say he preferred the streamlined plotting of the film - which makes the notion of people going on to buy the book in their millions just a little odd.

More recently, Kazuo Ishiguro's Never Let Me Go was re-released, with Keira Knightley on the cover to tie-in with the film version. Ishiguro might not have needed any further exposure - after all, the 2005 book was shortlisted for the Booker Prize - but he wouldn't have sniffed at his novel's return to the bestseller charts. Or at the many film reviews which said the book was probably better.

Increasingly, indeed, publishers - and authors - rely on film adaptations to sell novels. A look at the best-sellers of 2010 actually makes for rather dispiriting reading for those who would prefer fiction to stand alone as an art form: full of Stephenie Meyer, Dan Brown and Stieg Larsson books, there's not one single novel in the UK top 20 that hasn't been or isn't to be adapted into a film.

So, thanks to clever publishing contracts that often sell film and book rights simultaneously, the chances of somebody "doing a Palahniuk" and shooting to fame some years later is rare these days. Martin is enjoying his crossover success, but had already sold millions of books. Genuine publishing surprises are often found when long-lost books from underrated authors are found in the hands of television or film characters, becoming part of the storyline.

In recent years, Ayn Rand's 1957 novel Atlas Shrugged outsold Barack Obama's Audacity of Hope - at the height of the American president's popularity, no less - thanks to regular references to its brilliance in the hit US drama Mad Men. When Kristin Scott Thomas read a tale by Herodotus in The English Patient, sales of his Histories - 1,500 years old - shot up by 450 per cent. And demand for Louis De Bernières' Captain Corelli's Mandolin skyrocketed after Hugh Grant was seen relaxing with the book in Notting Hill.

Meanwhile Martin, this year voted one of Time Magazine's 100 most influential people, looks set to become even more influential in the future.