After restoration work, the copy will be displayed in the archives’ exhibition on the road to American independence, which opened last month.

Saul Nassé, executive director of the National Archives, hailed the find as “an extraordinary discovery.”

He added: “It is an increasingly rare copy of the Declaration of Independence, found not in the United States, but here in the United Kingdom.”

The document was seized by the Royal Navy on Christmas Eve 1776, when the HMS Raisonable captured an American ship, the Dalton, off the coast of Portugal after a seven-hour chase.

Dr Graham Moore of the National Archives said the discovery is “one of the rarest forms of Declaration we know of”, adding that it was not intended to be preserved due to the intention to distribute it quickly.

“After the original printing on July 4, news of the Declaration travels rapidly across North America and is reprinted as it reaches each successive colony,” he told BBC News.

“The copy we have is one of 11 surviving copies of those first printed in New Hampshire.”