At least 150 valuable antiquarian books on Japanese studies and art kept at the Japanese Embassy in London were stolen by a British man entrusted with the collection over the past three years, sources close to the case said Monday.

The man, who managed the library, has owned up to most of the charges against him.

However, recovery of the works, which are part of a collection maintained by the Japan Society, will be difficult because they have already been sold or auctioned off, the sources said, adding that the combined market value of the books and artwork runs into the tens of millions of yen.

The Japan Society, led by former British Ambassador to Japan John Whitehead and Lord Trenchard, comprises scholars on Japanese studies in Britain, with Japanese Ambassador to Britain Sadayuki Hayashi serving as honorary president.