Collection gathered by German advisers to Qing court being sold

Separately, the auction's highlight lot is a Qianlong-era monumental Hotan green jade washer that is said to be among the most impressive jade vessels remaining in a private collection. The piece is thought to be the largest jade basin recorded. It has been estimated to sell for between 600,000 and 800,000 pounds.

Henry Howard-Sneyd, Sotheby's chairman of Asian art, Europe and Americas, said: "This extraordinary washer has been in the same English collection since the 19th century, it has been published in one of the most famous books on jade, and it has been shown in the great exhibition at the Royal Academy in London in the 1930s, so it has a history, but since 1936 it has not been seen in public so it's a discovery as well."

The Important Chinese Art sale at Sotheby's London takes place on Wednesday.