A copy of the First Folio edition of William Shakespeare’s plays on display at Sotheby’s, London, on Thursday. (Reuters)

London, March 30 (Reuters): A complete First Folio edition of William Shakespeare’s plays, in prime condition and still in its 17th century calf leather binding, is expected to fetch up to ?3.5 million ($6.10 million) when it goes on sale in July.

Hailed by auctioneer Sotheby’s as the most important book in English literature, the First Folio is credited with saving for posterity many of the bard’s plays including Macbeth, Twelfth Night and Julius Caesar which had never before been printed.

“The First Folio preserves 18 of his plays, including some of the most major, which otherwise would have been lost for all time,” English literature specialist Peter Selley said as the volume was put on show today.

“Relatively complete copies of the Folio in contemporary or near contemporary bindings very rarely come to market. There is only one copy recorded as remaining in private hands,” he added.

Printed in 1623, seven years after Shakespeare’s death and containing 36 plays, only about 250 copies of the First Folio survive and most of those are incomplete.

The volume up for sale on July 13 has been in the William’s Library ? a key research facility for English Protestant dissent ? since about 1716, making it the longest uninterrupted ownership by a public library of any copy in the world.

Daniel Williams, the leading dissenting minister of his time, acquired the Folio when he bought the library of fellow nonconformist William Bates.

The thick tome with its heavy, yellowing pages and portrait of England’s leading playwright on the front is not only unique for its completeness and condition.

It contains detailed notes in the margins made, it is believed, by contemporary scholars and giving an insight into the understanding and interpretation of the wordsmith’s masterworks soon after his own era.