A copy of the world's most expensive book, which features life-sized prints of flamingoes and swans, is tipped to fetch up to six million pounds at auction in Britain, Sotheby's said on Thursday.

John James Audubon's seven-volume Birds Of America, which dates from the 19th century, will be sold alongside literary treasures like a copy of William Shakespeare's First Folio and a series of letters by Queen Elizabeth I.