Staff at the library have discovered that up to 600 supposedly ancient Chinese texts from their 15,000-strong archive were found to date from closer to 1940 than AD400.
New tests, carried out as part of a process to log the collection onto a digital database, revealed that many stemmed from a counterfeit operation run by Shengduo Li and his family from the turn of the century.
Mr Li's scam is believed to have begun in 1911 when he persuaded a Chinese official to divert to his house an ox cart transporting a large collection of real manuscripts from the Silk Road site of Dunhuang to the National Library of China.
This grew, until he masterminded an operation forging copies by the hundred, with serial numbers on the authentic manuscripts being altered to tally with the forgeries. His reputation as an eminent collector apparently made him immune to question. Some of the fakes are believed to have been produced after his death in 1935.
The manuscripts were discovered as a result of the transfer of the collection onto a digital database. Japanese scholars, who had limited access to their own manuscripts, had come to compare their own copies with the British Library's and discovered a number of clues.
"The level of sophistication of the forgeries is quite interesting. But it's not surprising, as the Chinese have a long tradition and tend to do things as they have for hundreds of years, such as paper-making and calligraphy," said Dr Susan Whitfield, the British Library's curator of Chinese manuscripts.
"There was a lot of turmoil at the time they were made, so the fact that they could still find time is surprising. But they still fell down, sometimes in trying to be too clever. For example, using forms of words that date from BC200 rather than AD400," Dr Whitfield added.
"You would have to be a real scholar to know the difference between those two. Many people have been fooled, and many continue to be fooled."
The fake manuscripts are scrolls, imitating the genuine versions of calligraphy on dyed yellow paper. One of the newest clues to their lack of veracity has been provided by a method perfected at Queen's University, Belfast, which can detect whether the paper has been dyed with a bark derivative from the amur cork tree, as with the real items.
Dr Whitfield stressed yesterday that Shengduo Li was not the only person involved in faking Chinese manuscripts, and that "many local figures" were also involved.
The Chinese themselves, she said, were relaxed about the find, as they had a large number of originals. The Japanese, who had a much smaller collection, were "sensitive" about it. The findings will be discussed at a closed conference of specialists next week.
The fate of the faked manuscripts is not uncertain. "We will keep them out of curiosity value. They are still manuscripts of up to 100 years old and interesting in themselves for a whole lot of other reasons, like technology, paper-making in the 20th century," she said. "For some scholars that may actually be more interesting."Reuse content