For years it has been the subject of bitter controversy, its existence repeatedly claimed but never officially acknowledged.
At last, the leaked draft of a report to be published next week by the European parliament removes any lingering doubt: Echelon, a shadowy, US-led worldwide electronic spying network, is a reality.
Echelon is part of an Anglo-Saxon club set up by secret treaty in 1947, whereby the US, UK, Canada, Australia, and New Zealand, divided the world between them to share the product of global eavesdropping. Agencies from the five countries exchange intercepts using supercomputers to identify key words.
The intercepts are picked up by ground stations, including the US base at Menwith Hill in North Yorkshire, and GCHQ's listening post at Morwenstow in Cornwall.
In the cold war, eavesdropping - signals intelligence, or Sigint as it is known in the trade - was aimed at military and diplomatic communications. Helped by increasingly sophisticated computers, it has now switched to industrial, commercial targets - and private individuals.
Echelon computers can store millions of records on individuals, intercepting faxes, phone calls, and emails.
The MEP's report - which faced opposition from the British and American governments and their respective security services - was prompted by claims that the US was using Echelon to spy on European companies on behalf of American firms.
France, deeply suspicious of Britain's uniquely close intelligence links with the US, seized on reports that Echelon cost Airbus Industrie an £8bn contract with Saudi Arabia in 1994, after the US intercepted communications between Riyadh and the Toulouse headquarters of Airbus - in which British firms hold a 20% stake.
The MEPs admitted they had been unable to find conclusive proof of industrial espionage. The claim has been dismissed by all the Echelon governments and in a new book by an intelligence expert, James Bamford.
More disturbing, as Mr Bamford and the MEPs pointed out, was the threat Echelon posed to privacy. "The real issue is whether Echelon is doing away with individual privacy - a basic human right," he said. The MEPs looked at statements from former members of the intelligence services, who provided compelling evidence of Echelon's existence, and the potential scope of its activities.
One former member of the Canadian intelligence service, the CSE, claimed that every day millions of emails, faxes and phone conversations were intercepted. The name and phone number of one woman, he said, was added to the CSE's list of potential terrorists after she used an ambiguous word in an innocent call to a friend.
"Disembodied snippets of conversations are snatched from the ether, perhaps out of context, and may be misinterpreted by an analyst who then secretly transmits them to spy agencies and law enforcement offices around the world," Mr Bamford said.
The "misleading information", he said, "is then placed in NSA's near-bottomless computer storage system, a system capable of storing 5 trillion pages of text, a stack of paper 150 miles high".
Unlike information on US citizens, which officially cannot be kept longer than a year, information on foreigners can he held "eternally", he said.
The MEP's draft report concludes the system cannot be as extensive as reports have assumed. It is limited by being based on worldwide interception of satellite communications, which account for a small part of communications.
Eavesdropping on other messages requires either tapping cables or intercepting radio signals, but the states involved in Echelon, the draft report found, had access to a limited proportion of radio and cable communications.
But independent privacy groups claimed Britain, the US and their Echelon partners, were developing eavesdropping systems to cope with the explosion in communications on email and internet.
In Britain, the government last year brought in the Regulation of Investigatory Powers Act, which allowed authorities to monitor email and internet traffic through "black boxes" placed inside service providers' systems. It gave police authority to order companies or individuals using encryption to protect their communications, to hand over the encryption keys. Failure to do so was punishable by a sentence of up to two years.
The act has been condemned by civil liberties campaigners, but there are signs the authorities are keen to secure more far reaching powers to monitor internet traffic.
Last week, the London-based group, Statewatch, published leaked documents saying the EU's 15 member states were lobbying the European commission to require that service providers kept all phone, fax, email and internet data in case they were needed in criminal investigations.
© Guardian Newspapers Limited 2001