A "teaser card" carrying clues to the plot of the long-awaited fifth Harry Potter book sold yesterday for £28,000 at a charity fundraiser.

The card, which was handwritten by JK Rowling, was bought by a private American collector for six times its reserve price at Sotheby's in London.

An internet group which organised a worldwide whip-round to try to secure a sneak preview was outbid when it offered just over £15,000.

The author wrote 93 words on a card, giving a glimpse of what the future holds for the boy wizard and friends in Harry Potter and the Order of the Phoenix.

The card also contains the author's signature.

Ms Rowling wrote the card at a Society of Authors conference this year where writers were asked to try to raise money for Book Aid International, which provides around 750,000 books each year for more than 40 poor countries.

• A Swindon woman, Monica Timms, who bought a hardback copy of the then unknown Harry Potter and the Philosopher's Stone five years ago for £10.99, sold it for £13,000 at an auction.