A cache of letters, including one from Queen Elizabeth I criticizing the imprisoned Mary, Queen of Scots, goes under the hammer at Sotheby's on Tuesday.
The papers, unknown to historians and biographers, include four letters signed by Elizabeth and others penned by leading political figures and addressed to Sir Ralph Sadler, who was entrusted with the custody of Mary in 1584 and 1585.
They form part of an auction of books, manuscripts and drawings from the collection of Lord Hesketh, who died in 1955, which is expected to fetch 8-10 million pounds ($13-$16 million).
The highest price is likely to be set by renowned 19th century ornithologist and painter John James Audubon's "Birds of America," one of 11 copies held in private hands which is estimated to be worth 4-6 million pounds.
A copy of the same work containing hand-colored, life-size prints of birds was sold in 2000 by Sotheby's rival Christie's and set a world record price for a printed book of $8.8 million.
"Most of these objects are collectors' items, but for the Mary, Queen of Scots letters there might be some institutional interest at auction," said Sotheby's specialist David Goldthorpe who is in charge of the sale.
"Although the phrase is overused, they are genuinely unique," he told Reuters.
Possibly the most important of the 40 or so letters relating to Mary is one from Elizabeth dated October 31, 1584 in which she criticizes her rival in remarks intended to be shown or read to the Scottish queen.
Among her observations, the English monarch writes of Mary's "sundry hard and dangerous coorses heald towardes us."
There are several letters from Elizabeth's chief minister Lord Burghley and spymaster Francis Walsingham. The bundle is expected to fetch 150-200,000 pounds.
The auction also includes a book widely regarded as the most important in all English literature — the first collected edition of Shakespeare's plays, "First Folio," dated 1623.
The First Folio, with 36 plays including "Macbeth," "The Tempest," and "Twelfth Night," is expected to sell for between 1.0 and 1.5 million pounds ($1.5-$2.3 million) and is one of only 21 privately-owned copies, according to the auctioneer.