A "vanishingly rare" copy of the Declaration of Independence has been found in London, dug up in archives holding documents from the British capture of an American privateer ship in 1776, just as the United States celebrates its 250th anniversary.

A flawed first copy — dashed off in an all-nighter in 1776 — endures as a template for democracy in action.

Nearly 250 years before the Declaration of Independence became one of the world’s most recognizable political documents, it was simply breaking news. According to the Harvard…