A rubber (eraser) belonging to Britain's late Princess Diana is up for auction. The eraser - which measures five inches by two inches and is stamped with the words "For BIG mistakes" - was used by the Princess of Wales when she was a nine-year-old schoolgirl at Riddlesworth Hall boarding school in Diss, Norfolk.

The royal personalized the item with the words "D. Spencer," "Diana," "Riddlesworth Hall" and "Diss" and the phrase "Bomb Beware Help" in her own handwriting.

The unique piece of stationary is expected to fetch over Ł300 [$494] when it goes under the hammer in Colchester, Essex, next week.

Diana - who died in a car crash in Paris in 1997 - kept the rubber as a memento of her years at the boarding school, and took it with her to Buckingham Palace when she married Prince Charles in 1981.

It was eventually given away to Jane Parsons, a secretary who worked in her private office.

Around 150 other pieces of royal memorabilia will also be sold in the auction at Reeman Dansie auctioneers. Other lots include a personal note from Diana to Jane Parsons, thanking her for giving evidence in the trial of Michael Fagan, who famously broke into Buckingham Palace and sat on Queen Elizabeth's bed in 1982.

The handwritten note reads: "Dear Jane, I just wanted you to know that I thought of you on Thursday at the Old Bailey - it cannot have been a very nice experience but I was told that you coped brilliantly!"

"It is bad enough having to make a speech but to give evidence must be very daunting! You are marvelous to have gone through the ordeal and well done! Yours sincerely, Diana."