A vanishingly rare copy of the US Declaration of Independence has been discovered by a volunteer at the National Archives in Kew, west London. Michael Scurr, who was cataloguing 18th-century Royal Navy correspondence, came across the document, which was printed 250 years ago in New Hampshire. The discovery is considered a thrilling find, as it is one of only 11 known surviving copies of the "Exeter printing" and the only one known outside the United States.