The revelations are the result of a joint investigation involving the Munich-based German national newspaper Süddeutsche Zeitung, the German public broadcasting stations WDR and NDR, as well as the British private television station Channel 4.
Previously unreleased documents examined by the journalists involved as well as experts consulted in the course of their investigation indicated that the British intelligence agency GCHQ was able to access underwater telecommunications cables owned by Cable & Wireless. It was purchased by Vodafone in 2012.
The reports said that Cable & Wireless was part of a GCHQ program known as "Mastering the Internet," in which private companies cooperated with British intelligence gatherers to help them tap into Internet traffic data.
The Snowdon documents, which refer to Cable & Wireless by the pseudonym "Gerontic," showed that the company provided access to around 30 underwater cables, allowing it to gather data on millions of internet users around the globe.
The Channel 4 report alleged that Cable & Wireless rentered space to GCHQ to access a cable linked to the southern English region of Cornwall.
According to the Süddeutsche report, some of the documents indicate that in 2009 around 70 percent of the Internet data gleaned by GCHQ was accessed via Cable & Wireless, before it was purchased by Vodafone. They also show that the Cable & Wireless was paid six million pounds, (7.5 million euros, $9.4 million) in return.
GCHQ declined to comment on the Channel 4 report.
'No unlawful activity'
Asked by Channel 4 about the documents, Vodafone issued a statement saying that it had found no evidence of any wrongdoing by Cable & Wireless.
"We have found no indication whatsoever of unlawful activity within Vodafone or Cable & Wireless and we do not recognise any of the UK intelligence agency programmes identified," the statement said. "Furthermore, Vodafone does not own or operate the cables referred to."
Previously classified documents leaked by Edward Snowden since mid-2013 have revealed the previously unknown scale of mass surveillance conducted by the US National Security Agency and other spy agencies, including the GCHQ, on private citizens and politicians alike.
Both the NSA and GCHQ are part of the so-called "five eyes" intelligence cooperation alliance, which also includes spy agencies in Australia, New Zealand and Canada.
A revelation that the NSA tapped into German Chancellor Angela Merkel's cellular phone caused considerable consternation in Berlin last year.
Snowden currently resides in Russia, which has granted him temporary residency after he fled there on the run from US authorities, which want to put him on trial on a series of charges.
pfd/ipj (dpa, Reuters)