Insights into activities of GCHQ in gathering billions of pieces of data from fiber-optic cables come from two documents, "Mastering the Internet" and "Global Telecoms Exploitation," The Guardian reported Friday.
Snowden is the ex-contractor for the U.S. National Security Agency who has been a fugitive since revealing the secret intelligence-gathering work of the NSA spying program Prism earlier this month.
The GCHQ, or Government Communications Headquarters, records phone calls and stores the contents of e-mail messages, Facebook posts and the history of what websites were accessed by an Internet user.
British officials claim the spying program "produces larger amounts of metadata than NSA."
While the British public was not aware of the program, a source familiar with intelligence gathering told The Guardian the data has been collected legally and that the intercepted information had led to a number of thwarted terror attacks, including one on the 2012 Olympics.
Trials of the program began in 2008 and by May 2012 300 analysts from GCHQ and 250 from NSA had been assigned to the program.
Snowden's documents indicate that by last year, the British intelligence agency was receiving 600 million "telephone events" each day. It also had tapped more than 200 fiber-optic cables, and could process information from 46 of them at a time.
The tapped cables have the theoretical capacity to carry data equivalent to transmitting the 14 million books in the British Library 192 times in 24 hours.
While GCHQ collects "a vast haystack of data," it is looking for "needles," the source said.
"We are not looking at every piece of straw," the source added, but rather for information about security, terror, organized crime and "economic well-being."
The documents indicate GCHQ is expanding its capabilities in order to handle data from new cables that carry data at 100 gigabits a second.