A British spy agency taps the network of cables that carry the world’s internet and telephone communications to secretly collect vast streams of private information, documents leaked by the whistleblower Edward Snowden has revealed.

The GCHQ agency scoops as much as it can from Facebook posts, email messages, internet histories and calls while tapping into the global fibre-optic network with little legal oversight, according to a report from the Guardian newspaper.

The activities are detailed in two documents leaked to the newspaper by Snowden, the former NSA and CIA worker who revealed America was spying on millions of foreigners and US nationals without their knowledge under the Prism scheme. The GCHQ scheme is billed as wider-ranging than Prism, with less legal oversight.

Snowden provided the Guardian with two GCHQ documents, titled Mastering the Internet and Global Telecoms Exploitation, which detail how an operation codenamed “Tempora” has for 18 months gathered, stored and analysed vast amounts of data, while also passing information to its US counterpart, the National Security Agency.

"It's not just a US problem,” Snowden told the newspaper. “The UK has a huge dog in this fight. They are worse than the US."

Intelligence superpower

The Guardian says the programme has turned the UK into an "intelligence superpower" among members of the Five Eyes electronic spying alliance of US, UK, Canada, Australia and New Zealand.

The leaked documents show that the GCHQ intercepted 600 million "telephone events" each day last year by tapping more than 200 fibre-optic cables. Hundreds of analysts from the GCHQ were assigned to sift through the intercepts, with lawyers saying the UK had “a light oversight regime compared with the US", according to Snowden.

A source defended the programme, saying it was searching for needles rather than examining the entire haystack.

"We are not looking at every piece of straw. There are certain triggers that allow you to discard or not examine a lot of data so you are just looking at needles. If you had the impression we are reading millions of emails, we are not. There is no intention in this whole programme to use it for looking at UK domestic traffic – British people talking to each other."

The source told the newspaper that the tapping of the cables was conducted under secret agreements with commercial firms, and that some had been paid for their co-operation, and their licences to operate were dependent on agreeing to be part of the programme.

According to GCHQ's legal advice, detailed in the newspaper, it was able to launch Tempora by using a clause in the 2000 Regulation of Investigatory Powers Act (Ripa), which allows the foreign secretary to sign a warrant for the interception of swathes of material as long as one end of the monitored communications is abroad.

As much of the information sent through fibre-optic cables bounces around the world before returning to source, many UK-specific communications are technically subject to the clause.