Only six copies of the book are in private hands

The First Folio of Comedies, Histories and Tragedies was sold at Bloomsbury's in London on behalf of Anne Humphries.

The first edition was one of only 600 copies of the book printed in 1623, with only 300 thought to still exist.

The book had 40 pages missing, including most of The Tempest play. A complete version sold in 2001 for �4.1m

Mrs Humphries, from Greater Manchester, inherited the book in September after she was tracked down by a genealogist as the closest living relative of Frances Cottle of Tottenham, London.

It had been gathering dust in Ms Cottle's home until her death in 2002. It took two years for the genealogist to track down a relative.

Mrs Humphries, 48, said she hoped the book had been bought by a public institution, although the identity of the successful bidder is not yet known.

She said: "This is tremendous, it's such an important piece of literature and the history that surrounds it, it really needs to be documented.

Published posthumously

Mrs Humphries hopes the book was bought by an institution

"It would not have been right to just hold it in a cupboard. There are so many people out there who could get so much pleasure from this book."

The book was published seven years after the death of Shakespeare.

It was not a commercial success despite containing 18 new plays.

"All other Shakespeare folios have been logged and registered so they know where they are around the world," said a Bloomsbury spokesman.