However, on Friday a source with knowledge of intelligence argued that the data was collected legally under a system of safeguards, and had provided material that had led to significant breakthroughs in detecting and preventing serious crime.Britain's technical capacity to tap into the cables that carry the world's communications – referred to in the documents as special source exploitation – has made GCHQ an intelligence superpower.By 2010, two years after the project was first trialled, it was able to boast it had the "biggest internet access" of any member of the Five Eyes electronic eavesdropping alliance, comprising the US, UK, Canada, Australia and New Zealand.UK officials could also claim GCHQ "produces larger amounts of metadata than NSA". (Metadata describes basic information on who has been contacting whom, without detailing the content.)By May last year 300 analysts from GCHQ, and 250 from the NSA, had been assigned to sift through the flood of data.The Americans were given guidelines for its use, but were told in legal briefings by GCHQ lawyers: "We have a light oversight regime compared with the US".