They flow deep underneath the Atlantic Ocean and into the United Kingdom below the golden sands of idyllic beaches. But the internet cables that come ashore at the coast of Cornwall, England, are not just used to connect the country with the rest of the world.

According to new reports based on documents from National Security Agency whistleblower Edward Snowden, the cables have become an integral part of the global mass surveillance system operated by the British spy agency Government Communications Headquarters, intimately assisted by a company now owned by Vodafone, the world’s third largest cellphone network provider.

The latest details about the extent of the spying were revealed on Thursday by the British Channel 4 News, the German newspaper Süddeutsche Zeitung, and the German broadcaster WDR, who worked in partnership with Intercept founding editor Laura Poitras. The Intercept obtained a preview of the revelations in advance of their publication.

According to the reports, British telecommunications firms have helped GCHQ dramatically scale-up the volume of internet data it collects from undersea cables. In the five years leading up to 2012, there was a 7,000-fold increase in the amount of data the agency was sweeping up, with its computers monitoring some 46 billion private communications “events” every day, according to documents cited in the reports. The data swept up from the cables would include content from emails, online messages, browsing sessions, and calls made using internet chat tools.

British telecommunications company Cable & Wireless played a leading role in the secret cable tapping operation, according to the reports, and the collaboration appears to have gone further than simply complying with the law in helping implement the surveillance.

The company provided GCHQ with updates on opportunities it could give the agency to tap into internet traffic, and in February 2009 a GCHQ employee was assigned to work within Cable & Wireless in a “full-time project management” role. The British government paid Cable & Wireless more than £5 million ($9 million) of taxpayers’ money as part of an annual lease for GCHQ to access the cables. The agency described the company a “partner” and designated it the codename Gerontic.

According to the reports, Cable & Wireless also appears to have helped GCHQ obtain data from a rival foreign communications company, India’s Reliance Communications, enabling the spies to sweep up communications sent by millions of internet users worldwide through a Reliance-owned cable that stretches from England across Asia and the Middle East. This so-called “access point” for GCHQ was named Nigella and located near an agency surveillance base in Bude, Cornwall (pictured above). Reliance did not respond to a request for comment.

In July 2012, the multinational phone company Vodafone bought Cable & Wireless for about $1.5 billion. The documents indicate that the Nigella surveillance access point remained active as of April 2013.

Vodafone said in a statement that it complies with the law and does not give “direct access” to its cables. The company says it is compelled to provide certain access to data based on warrants issued by the government.

“There are processes for us to do that [comply with warrants] which we’re not allowed to talk about because the law constrains us from revealing these things,” said Vodafone spokesman Matt Peacock in a statement to Channel 4 News. “We don’t go beyond what the law requires.”

GCHQ declined to comment, saying in statement that “we do not comment on intelligence matters” and that “all of GCHQ’s work is carried out in accordance with a strict legal and policy framework, which ensures that our activities are authorized, necessary and proportionate.”

Update, Nov. 25, 2014 at 17:15 EST: On Tuesday, the German newspaper Süddeutsche Zeitung published a series of GCHQ documents from Snowden related to the Cable & Wireless surveillance operation. Those documents can be downloaded here, or here.

Photo: PeterJDH/Flickr