A first edition copy of Harry Potter and the Philosopher's Stone, annotated by author JK Rowling, will sell at Sotheby's charity auction First Editions, Second Thoughts, which is to be held on May 21 in London.

This annotated copy, which also includes Rowling's drawings, should comfortably beat the record for a Potter first edition set in April

The sale offers 50 contemporary first editions, all of which have been annotated by their authors. The Harry Potter book sees Rowling revealing:

"I wrote the book in snatched hours, in clattering cafes and or the dead of night. For me, the whole story of how I wrote Harry Potter and the Philosopher's Stone is written invisibly on every page and legible only to me."

She also shares the story of how Quidditch was invented, stating that it "was invented in a small hotel in Manchester after a row with my then boyfriend.

"I had been pondering the things that hold a society together, cause it to congregate and signify its particular character and knew I needed a sport."

Harry Potter is one of the few modern first edition books to have proved its worth as a collectible already, with the auction record for a first edition, first printing copy being set at Heritage Auctions' at $26,046 in April.

Collectors can now bid on a copy of Harry Potter and the Prisoner of Azkaban signed by Daniel Radcliffe and Emma Watson at PFC Auctions.