LONDON (AP).- The British Museum says it is getting 25 million pounds ($38 million) from John Sainsbury, the former chairman of Britain’s eponymous supermarket chain. The donation is one of the biggest gifts to the arts in recent decades and will help the world-renowned London institution fund an extension and preserve its cache of ancient artifacts. The donation also comes at a time of uncertainty for British cultural institutions, which are facing deep cuts in public funding as the new government works to balance the country’s budget. The British Museum receives about 5 million visitors a year. Its collection includes the Rosetta Stone, the Lewis Chessmen, and the Elgin Marbles.