A brand new leak by the Guardian reveals that the top British GCHQ is tapping directly into global telecommunication networks for secret access to the majority of the world's Internet communication, way more potent than what the NSA's PRISM program is capable of as well. The revelation came at the same time the U.S. government filed charges of espionage against Edward Snowden.

Britain's spy agency GCHQ has secretly gained access to the network of cables which carry the world's phone calls and internet traffic and has started to process vast streams of sensitive personal information which it is sharing with its American partner, the National Security Agency (NSA).

The sheer scale of the agency's ambition is reflected in the titles of its two principal components: Mastering the Internet and Global Telecoms Exploitation, aimed at scooping up as much online and telephone traffic as possible. This is all being carried out without any form of public acknowledgement or debate.

One key innovation has been GCHQ's ability to tap into and store huge volumes of data drawn from fibre-optic cables for up to 30 days so that it can be sifted and analysed. That operation, codenamed Tempora, has been running for some 18 months.

GCHQ and the NSA are consequently able to access and process vast quantities of communications between entirely innocent people, as well as targeted suspects.

This includes recordings of phone calls, the content of email messages, entries on Facebook and the history of any internet user's access to websites – all of which is deemed legal, even though the warrant system was supposed to limit interception to a specified range of targets.

The existence of the programme 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 programme of suspicionless surveillance in human history".

"It's not just a US problem. The UK has a huge dog in this fight," Snowden told the Guardian. "They [GCHQ] are worse than the US."

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.)