Its digital archives include records for 4.5 million items, or about half the collection. The patchiness of the catalog has been the subject of criticism for decades. In 1988, the National Audit Office, a government watchdog, said in a report that the museum’s stock-taking and inventories were “unsatisfactory.” Because of “continuing staff shortages” it was “impossible” to say when the situation would improve, the report added.

Charles Saumarez Smith, a former director of the Royal Academy of Arts, said that other major British institutions, including the Victoria and Albert Museum, had largely completed computerized inventories since that damning report. “The big question is, why didn’t the British Museum?” he said.

Osborne, the British Museum chairman, conceded in the BBC interview that inventory keeping was a problem and said that gaps in those records could be exploited. But he insisted that the museum’s global treasures were safe.

Even with such reassurances, lawmakers and museum administrators in Greece and Nigeria used the thefts as an opportunity to reiterate their calls for the return of the Parthenon Marbles, sometimes called the Elgin Marbles, and the British Museum’s collection of Benin Bronzes.

Many of the artifacts in the museum’s collection, which was founded in 1753, were obtained when Britain ruled large swaths of the world, and were acquired by colonial officials and soldiers, as well as traveling anthropologists and natural historians. For decades, some activists and academics have viewed the museum’s collection as a cultural extension of empire, often highlighting the most controversial items in its collection.

After the killing of George Floyd in the United States in 2020 and the rise of the Black Lives Matter movement, the museum’s collection came under even more intense scrutiny. It took some steps to highlight its links to slavery, including those of Hans Sloane, a physician whose collection formed the basis of the museum.