The most significant Michelangelo find in living memory - like finding part of the Holy Grail

James Miller, Sothebys

The sketch is said to date from between 1494 and 1504 and is regarded as a major work by one of the greatest artistic geniuses in history.

"There have been only three major Michelangelo drawings on the market in the last quarter century," said the director of Old Master Drawings at Sotheby's, Gregory Rubenstein.

"The last one that was sold went for a record price."

Importance

It was a Sotheby's expert, Julien Stock, who chanced upon the work while flicking through a scrapbook of Old Master drawings for an insurance evaluation.

At the time Sotheby's described the find as "the most significant Michelangelo find in living memory; like finding part of the Holy Grail".

The cost of insuring such a valuable work made it impossible to keep the drawing at Castle Howard, which was the setting for the TV series Brideshead Revisited.

Simon Howard, who owns Castle Howard said: "Clearly this is a drawing of major importance which has been accepted by all the experts and as such it should be on display in a national gallery or museum where everyone can enjoy it."

Michelangelo's famed sculpture - David

In March the National Galleries of Scotland launched an appeal to raise money to prevent the work from being sold to a private collector or abroad.

"We feel it is vital that this drawing goes on public display," said a spokeswoman for the National Galleries of Scotland.

Castle Howard has already sold three other paintings from its collection to the National Gallery of Scotland.

The drawing is similar to four other early figure drawings by the artist which are in museum collections in Paris, Munich, Vienna and London.

It is dated later than the others and is seen as an important link between them and Michelangelo's later work.

Michelangelo was a leading figure in the High Renaissanace and painted the ceiling of the Sistine Chapel in Rome as well as sculpting such works as David.