Bestselling epic fantasy author George RR Martin has sent his fans into a frenzy after announcing that he has written 1,261 pages of the long-awaited fifth volume in his Song of Ice and Fire series.

It is five years since Martin published the fourth novel in the epic series, set in a medieval-esque world where a wall of ice protects the land of Westeros, and the wait for A Dance with Dragons has prompted extraordinary levels of anticipation from readers. Some have even created a poster mimicking the Conservative party's new campaign, which shows David Cameron promising "vote for us and we'll ensure A Dance with Dragons is released in 2010". "I seem to have become a Tory campaign issue," wrote Martin in a message to his publisher.

Fans' vocal impatience for the next instalment reached such a pitch last year that Martin issued an angry statement to stem a rising tide of anger. "Some of you are angry about the miniatures, the swords, the resin busts, the games. You don't want me 'wasting time' on those, or talking about them here. Some of you are angry that I watch football during the fall," the author wrote. "Some of you don't want me attending conventions, teaching workshops, touring and doing promo ... After all, as some of you like to point out in your emails, I am 60 years old and fat, and you don't want me to 'pull a Robert Jordan' on you and deny you your book. OK, I've got the message. You don't want me doing anything except A Song of Ice and Fire. Ever. (Well, maybe it's OK if I take a leak once in a while?)"

Now, the author described as "the American Tolkien" by Time magazine has poked his head above the parapet again, telling fans that A Dance with Dragons has now become the second longest volume in his series, that he's been knocking off chapters and having "good, productive" days of writing. Huge excitement ensued from readers, but Martin attempted to douse the flames. "Jeez, guys. Calm down," he said on his blog. "This is why I hate to do updates. I say I have good day, and immediately I have 100 people deciding this means that Dance is finished. I'm not the oracle at Delphi ... When I finish Dance, you'll know it. I will write something like this: 'I have finished A Dance with Dragons.' You won't need to parse any hints."

But he failed to calm some readers down. "Where's the book, Mr Martin, where's the book? :) Here in Russia we are waiting, and waiting, and waiting," wrote one of the more eager fans.

Martin is not the only author to come under pressure from avid readers – and the fantasy genre appears to provoke particularly insistent readers. In his memoir On Writing, Stephen King related how he had been contacted by a sick old woman desperate to find out how his Dark Tower fantasy series ended before she died. Might King share his ending with her? The author said he had to tell her that he himself didn't know what was going to happen in the series, which eventually spanned seven books. The Robert Jordan referred to by Martin, meanwhile, is the author of the epic Wheel of Time fantasy series. He died after writing 11 Wheel of Time books, with the series currently being finished by author Brandon Sanderson.