File photo shows a First Folio edition of William Shakespeares' plays, dating from 1623 and considered to be one of the most important books in English literature, pictured at Sotheby's auction house in London on March 30, 2006.

A copy of William Shakespeare's First Folio, the first-ever compilation of the Bard's plays published in 1623, has been discovered in the library of a small town in northern France, a librarian said Tuesday.

One of the most valuable and coveted books in the world, the First Folio was uncovered when librarian Remy Cordonnier dusted off a book of Shakespeare's works dating to the 18th century for an exhibition on English literature in the town of Saint-Omer near Calais.

"It occurred to me that it could be an unidentified First Folio, with historicimportance and great intellectual value," he told AFP.

The copy of the book, which was published seven years after Shakespeare's death, was authenticated on Saturday by First Folio expert Eric Rasmussen from the University of Nevada.

"It is the 231st copy found in the world and the second in France," said Cordonnier.

The book, a compilation of 36 of Shakespeare's plays, is in good condition but missing about 30 pages, including the title page, which could explain how it went unnoticed for centuries.

Rasmussen wrote a book on the First Folio called "The Shakespeare Thefts" detailing his thrilling global hunt for what remains of the initial 750 copies of the book, a favourite for thieves across the centuries.

He describes "run-ins with heavily tattooed criminal street gangs in Tokyo, bizarre visits with eccentric,