Operation Tempora has been running for around 18 months and allows GCHQ to tap into and store huge volumes of data drawn from fibre-optic cables for up to 30 days. GCHQ is also sharing this sensitive personal information with its American partner, the National Security Agency (NSA) The existence of the program has been disclosed in documents shown to the Guardian by the NSA whistleblower Edward Snowden as part of his attempt to expose what he has called the largest program of suspicion less surveillance in human history.
Source: https://thehackernews.com/2013/06/Edward-Snowden-eavesdropping-fiber-cables-surveillance.html