The rare copy of Harry Potter and the Philosopher's Stone was discovered by a teacher 12 years ago along with two paperback first editions.

The anonymous seller found the books outside a school while tidying its library before an Ofsted inspection.

After the paperbacks went for £3,400 and £3,000, the seller said: "To say I'm pleased is an understatement."

They were sold during an online auction at Bishton Hall in Staffordshire earlier.

Only 500 hardback first editions of Harry Potter and the Philosopher's Stone were printed in 1997, most of which were sent to schools and libraries.

Image copyright Hansons Auctioneers

 Book expert Jim Spencer said the three copies "sparked intense bidding"

Prior to the auction the hardback had an estimate of £8,000-£12,000 due to some damage to its binding.

It was bought by a private UK buyer after "a tense auction battle", Hansons Auctioneers said.

It is the third copy of a hardback first edition found by the Derbyshire-based company in the last 12 months, and its book expert Jim Spencer described them as "the Holy Grail" for collectors.

"It was marvellous to see the Harry Potter books do so well and spark such intense bidding," he added.