It has been more than a decade since the spotlight was last shone on the operations being undertaken behind the high security fencing at Morwenstow, on the North Cornwall coast.
Then concerns were raised that the GCHQ satellite spy station was utilising the Echelon system to intercept phone calls, faxes and emails on behalf of the US and British security services.
Now the station – which is also said to be staffed by the US National Security Agency (NSA) – has been implicated in the latest privacy row about the collection and retention of internet and communications data.
Documents leaked to The Guardian by former US intelligence analyst Edward Snowden suggest GCHQ's "Mastering the Internet" programme got under way in 2007, resulting in an experimental research project, run out of the station near Bude, the following year.
Its purpose was to assess the uses of a so-called "internet buffer" – the interception and filtering of internet traffic coming into and out of the UK.
The project is thought to have developed into the current operation codenamed Tempora under which GCHQ is able to tap into cables and store internet and communications data for up to 30 days.
"Interesting" content is said to be stored for three days and metadata, such as information about who an email is from and to, for up to a month.
Many of the transatlantic fibre-optic cables carrying the digital traffic land in Cornwall, including one at Widemouth Bay. The current role played by the base at Morwenstow is not known.
Cheltenham-based GCHQ does not comment on intelligence matters but has insisted it is "scrupulous" in complying with the law.
But The Guardian said there were two principal components to the agency's surveillance programme, called Mastering the Internet and Global Telecoms Exploitation. It claimed the data was shared with the NSA.
The information regarding UK digital surveillance operations is the latest leak from Snowden, the former NSA contractor responsible for a string of disclosures about US intelligence tactics.
The American has admitted providing information to the news media about two highly classified NSA surveillance programmes.
The Guardian claimed Operation Tempora had been running for 18 months and GCHQ and the NSA are consequently able to access vast quantities of communications between innocent people as well as targeted suspects, including phone calls, the content of email messages, Facebook entries and a user's internet history.
Snowden, who is on the run seeking asylum, fled the US after deciding to reveal the NSA's secrets. He told the newspaper he wanted to expose "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," he said. "They (GCHQ) are worse than the US."
Documents provided to The Guardian revealed that by last year GCHQ was handling 600 million "telephone events" each day, had tapped more than 200 fibre-optic cables and was able to process data from at least 46 of them at a time.
GCHQ is also said to have accessed information about UK citizens via the NSA's secret Prism monitoring programme. A GCHQ spokeswoman said: "We do not comment on intelligence matters. Our intelligence agencies continue to adhere to a rigorous legal compliance regime. GCHQ are scrupulous in their legal compliance."
Sir Malcolm Rifkind, the Tory chairman of the Intelligence and Security Committee, has said he expects to receive a written report from GCHQ about the latest allegations. The committee is expected to launch an investigation into the latest revelations.
Foreign Office minister David Davis described reports that GCHQ lawyers told US counterparts there was a "light oversight regime" in Britain compared with America, as "worrying".
He said: "This reinforces the view that the oversight structure is wholly inadequate. Really what is needed is a full-scale independent judicial oversight that reports to Parliament."
However, Foreign Secretary William Hague has dismissed claims that it used Prism to circumvent the law as "baseless".
A leading civil liberties group has now requested a formal investigation into whether British intelligence services unlawfully accessed its communications.
Liberty said it had lodged a claim with the Investigatory Powers Tribunal over what it described as "out-of-control snooping".
It has asked the body to examine whether its human rights have been breached and whether official safeguards have been bypassed.
Liberty said it believes its electronic communications – and those of its staff – "may have been unlawfully accessed by the likes of the Security Services and GCHQ".
"Liberty will ask the Investigatory Powers Tribunal (IPT) whether the British Intelligence Services have used Prism and/or Tempora to bypass the formal UK legal process which regulates the accessing of personal material," it announced.
It has issued a claim "contending that rights under Article 8 of the Human Rights Act (the right to respect for one's private and family life, home and correspondence) have been breached".
Legal director James Welch said: "Those demanding the Snoopers' Charter seem to have been indulging in out-of-control snooping even without it – exploiting legal loopholes and help from Uncle Sam.
"No-one suggests a completely unpoliced internet but those in power cannot swap targeted investigations for endless monitoring of the entire globe."
Similar concerns about privacy were raised in 2001 when the European Parliament published a report into the Echelon eavesdropping system following a year-long inquiry.
It said the Echelon system was set up by the US and the UK during the Cold War with the help of Canada, Australia and New Zealand, to intercept communications sent by satellite but had moved on "to intercept private and commercial communications, not military communications".
There were also concerns that the base could help the United States conduct industrial espionage against European countries.
It concluded that there was a risk that activities at Morwenstow may breach the European Convention on Human Rights although no further action was ever taken.