JK ROWLING'S next major project is set to feature a charismatic hero who uses magic powers to overcome diabolical and grotesque adversaries.

Yet the next chapter of the author's literary career is expected to focus on Orpheus rather than Harry Potter.

Edinburgh-based publishing firm Canongate has offered Rowling the chance to retell the adventures of the legendary Greek hero, who is best known for attempting to rescue his wife Eurydice from the underworld.

Rowling has already expressed an interest in covering the classics after her studies in Greek and Roman mythology at Exeter University in the 1980s, and now Canongate has invited her to become its latest celebrity writer to contribute to its best-selling Myths series.

Early sales figures showed that Harry Potter And The Deathly Hallows, the seventh and final instalment of the series, flew off the shelves yesterday. WHSmith said that at one point it was selling 15 books every second - beating the 13-books-per-second record held by the previous Rowling volume, Harry Potter And The Half-Blood Prince.

Bookshops around the country opened their doors at midnight on Friday to Potter maniacs who had queued in their thousands.

Penning a book based on the classics might bring critical acclaim for Rowling, but the fee, which normally doesn't reach much higher than a five-figure sum for such works, would be a barely noticeable addition to her estimated £545m fortune.

A host of characters in the Harry Potter series - from Chiron the centaur to Fluffy the monstrous three-headed dog - were directly inspired by Rowling's love of ancient mythology.

A literary insider said: "She has expressed an interest in updating the story of Orpheus and Eurydice, but the whole thing is being kept under wraps so not to overshadow the launch of the final Harry Potter book."

It is understood that the invitation was made personally to Rowling by Canongate owner Jamie Byng. The publisher launched the acclaimed Myths series in 2005.

"From the outset, the idea was to approach top-class writers from all over the world and invite them to retell any myth in any way they chose," the insider said.

"In turn, their myths would be published all over the world. Already a wonderful array of writers have come on board, as have 24 superb international publishers."

There has been speculation that the end of the Potter series would allow Rowling to spend more time with husband Neil and her children, as well as dedicating more time to supporting her preferred charities: the Multiple Sclerosis Society of Scotland and Maggie's Cancer Care. But the chance to take on a literary classic could be too much for the author to resist.

Katherine Rushton, publishing reporter with literary journal The Bookseller, believes that Rowling will have another huge hit on her hands.

"People will go out and buy whatever JK chooses to write next, but updating Greek myths could be an inspired choice," she said.

"Mythology would provide that world of magic and fantasy that her readers have grown to love in the Harry Potter series.

"It would be fascinating to see how she interpreted classical myths and legends."

But Rushton believes the venture would not be without risks: "Whatever JK writes next, some people will be looking for an opportunity to criticise her and she will be put up for heavy scrutiny.

"She is going to have to make sure her next book is fantastic if she is going to retain her reputation. Harry Potter is a very hard act to follow."

Dr Jon Hesk, an expert in Greek literature at St Andrews University, feels Rowling is ideal to help bring the classics to the PlayStation generation.

"The magical element of classical mythology really seems to have made a big impression on JK Rowling, and Harry Potter is a hero in the Greek tradition," he said. "Because of her knowledge of classics, Rowling is ideally placed to re-examine the mythology of Orpheus.

"It would undoubtedly help introduce Greek mythology to a new, younger readership."

Hesk thinks Orpheus would be an ideal choice: "At the core of Orpheus is a tragic love story which is both classic and timeless. It is a lurid story with romance and horrible bloody death, and that is why it still fascinates people today.

"One of the reasons why JK Rowling might be interested in it is that there is a magical supernatural element as well.

"Orpheus was destined to face great challenges and mighty adversaries while developing his power, and that is something that chimes with the character of Harry Potter."

Authors who have had works published in the Myths series include Alexander McCall Smith, whose Dream Angus was based on Celtic legends, and Canadian Margaret Atwood, who told the story of Odysseus's wife, Penelope.