How Britain and the US keep watch on the world

From the National Security Agency's imposing headquarters at Fort Meade, Maryland, ringed by a double-chain fence topped by barbed wire with strands of electrified wire between them, America "bugs" the world.

Nothing politically or militarily significant, whether mentioned in a telephone call, in a conversation in the office of the secretary general of the United Nations, Kofi Annan, or in a company fax or e-mail, escapes its attention.

Its computers - measured in acres occupied by them rather than simple figures - "vacuum the entire electromagnetic spectrum", homing in on "key words" which may suggest something of interest to NSA customers is being conveyed.

The NSA costs at least $3.5bn (£1.9bn) a year to run. It employs at least 20,000 officers (not counting the 100,000 servicemen and civilians around the world over whom it has control). Its shredders process 40 tons of paper a day.

Its junior partner is Britain's Government Communications Headquarters (GCHQ) at Cheltenham, Gloucestershire, the eavesdropping organisation for which Katharine Gun worked. Like NSA, GCHQ is a highly secret operation. Until 1983, when one of its officers, Geoffrey Prime, was charged with spying for the Russians, the Government had refused to reveal what GCHQ's real role was, no doubt because its operations in peacetime were without a legal basis. Its security is maintained by massive and deliberately intimidating security.

Newspapers have been discouraged from mentioning it; a book by a former GCHQ officer, Jock Kane, was seized by Special Branch police officers and a still photograph of its headquarters was banned by the Independent Broadcasting Authority, leaving a blank screen during a World in Action programme. As with NSA, the size of GCHQ's staff at Cheltenham, about 6,500, gives no real indication of its strength. It has monitoring stations in Cyprus, West Germany, and Australia and smaller ones elsewhere. Much of its overseas work is done by service personnel.

Its budget is thought to be more than £300m a year. A large part of this is funded by the United States in return for the right to run NSA listening stations in Britain - Chicksands, Bedfordshire; Edzell, Scotland; Mentworth Hill, Harrogate; Brawdy, Wales - and on British territory around the world.

The collaboration between the two agencies offers many advantages to both. Not only does it make monitoring the globe easier, it solves tricky legal problems and is the basis of the Prime Minister's statement yesterday that all Britain's bugging is lawful. The two agencies simply swap each other's dirty work.

GCHQ eavesdrops on calls made by American citizens and the NSA monitors calls made by British citizens, thus allowing each government plausibly to deny it has tapped its own citizens' calls, as they do. The NSA station at Menwith Hill intercepts all international telephone calls made from Britain and GCHQ has a list of American citizens whose phone conversations interest the NSA.

The NSA request to GCHQ for help in bugging the diplomats from those nations who were holding out for a second Security Council resolution to authorise an attack on Iraq is unsurprising. Nor is it surprising that both organisations wanted to provide their political masters with recordings of private conversations of high-ranking international diplomats.

It is not difficult. Listening "bugs" can be planted in phones, electrical plugs, desk lamps and book spines. Given a clear line of sight, one device enables someone to detect and and interpret sound waves vibrating against the glass window panes of an office.

Bugging the world is not the problem. The problem is avoiding drowning in a sea of information. We should not be surprised that GCHQ and NSA eavesdrop on us. We pay them to do it. We should be asking: "Do they earn their keep?" And, unless we get a few more whistle-blowers like Ms Gun, we will not know, because both agencies surround themselves with a wall of secrecy.

WHO DO WE BUG?

Although under domestic law GCHQ needs a warrant from the Home Secretary to tap telephones in Britain, it can do so abroad without such authorisation.

But the United Nations headquarters in New York is considered sovereign territory, and placing a bug there would be illegal under international law.

Intelligence services spy on hostile and friendly countries, the latter mainly for commercial reasons, but also to gain an edge in diplomatic negotiations. Nato allies are not always immune from intelligence operations by Britain.

Staff working for the UN inspection teams in Iraq were convinced they were under surveillance.

France, Germany and Russia complained of a rise in espionage against them. There was intense activity directed at Jordan and Syria, as well as Saudi Arabia, Yemen and Egypt.

Officials say the only shock about Katharine Gun's discovery of an e-mail from the National Security Agency is that she was surprised by it.

Kim Sengupta