'We'd joke that the phones were bugged, but to hear it said like this is dismaying'

Step into the delegates lounge of the United Nations in New York on any weekday evening and you will see a throng of well-oiled diplomats propping up the bar. But some of them in their Armani suits and crocodile shoes are not proper diplomats. They have gathered for duty-free tipple,cigars and the opportunity to swap secrets at one of the world's richest seams of intelligence.

Some of them must have choked on their gin and tonics last night as they digested the news that had the UN building humming: Clare Short's claim that Britain had bugged the office of Kofi Annan.

Even though aides to the UN secretary general, had suspected that wiretaps went on, the bold assertion that agents from such a trusted ally had betrayed the trust of their Ghanaian boss came as a shock. Shashi Tharoor, the senior Annan adviser, said: "We would jokingly say to each other that the phones were bugged, but to hear it in this form is deeply dismaying."

The UN delegates lounge is the hub of many spying operations. It is where an MI6 agent, working undercover as an accredited diplomat, can chat to what he hopes is a corruptible Chinese delegate about North Korea's secret nuclear programme. It is where Saddam Hussein's not-so-secret agents rubbed shoulders with the Russians and the French.

After a tough negotiating session in the UN Security Council, what better place to linger than the delegates lounge to glean the inside story of what really went on behind closed doors.

At times of international crises, the United Nations becomes a fount of vital diplomatic information which the attentive spy can channel back to his government as a matter of urgency. For UN officials, already paranoid about leaks, the need for confidentiality is paramount. But for intelligence agents from across the globe, the main target must always have been the UN secretary general, in this case Mr Annan, who presides over a buzzing hive of diplomatic activity from his 38th floor office.

For Britain and the US, who were trying to win UN backing for the war on Iraq, the benefits of intercepting Mr Annan's private conversations with foreign ministers, heads of state and ambassadors would have been incalculable. The UN has other sensitive information. Raw intelligence is collated from UN officers worldwide before being turned into reports for the UN Security Council. The council - and particularly its permanent five with veto power - has to take decisions about war and peace based on Mr Annan's recommendations, distilled from the confidential reports.

Some UN departments, such as the UN weapons inspectors on the 31st floor, are privy to raw intelligence from the major powers, including the CIA and MI6. What a boon for the Iraqis, before the fall of Saddam, when they were able to eavesdrop on the UN inspectors with a little help from their friends.

Ms Short's comments, although shocking, did not surprise anyone at UN headquarters, where officials take it for granted that spying is part and parcel of international diplomacy. "What bombshell?" said one senior UN official, while awaiting Mr Annan's reaction, after the secretary general's return from Japan. "We'd always assumed that [spying] goes on all the time."

Joseph Legwaila of Botswana, the former Security Council ambassador who now knows that his hotel room in London was bugged by the British when he was a delegate to the Lancaster House negotiations on Rhodesia, said: "You always worry about wiretaps but we thought that sometimes it was better for them to get the truth straight from the horse's mouth, as it were." But he added that he would be "horrified" if Mr Annan's office had been bugged.

Another senior European diplomat said he was "deeply shocked" by the claim, which came on the heels of the collapse of the Katharine Gun court case into the bugging of six "undecided" Security Council members by the US and Britain in the critical days before the Iraq war. The diplomat said: "It's the fact that it's the coalition [US and Britain] sharing the task once again. It's one thing to bug six ambassadors, but it's another to do it to the UN secretary general. There's going to be uproar in public opinion here."

Ms Short did not explain how the alleged eavesdropping had been organised in Mr Annan's office: It is not known whether she was referring to a conventional telephone wiretap, a bugging device placed in his office, or a sophisticated satellite intercept. But she did say that, "in the case of Kofi's office, it's been done for some time".

The UN said yesterday that UN security staff regularly "swept" the secretary general's office for bugs to prevent intercepts of sensitive information. But "frankly we're out of our league," said a senior UN official. Electronic eavesdropping is not the only tool available to the intelligence services. At the UN, their weapon of choice must be human intelligence.

Governments lobby hard to place their people in influential positions in the UN secretariat. The most sensitive jobs are the subject of the heaviest lobbying: At present, the head of UN political affairs is British; the head of peace-keeping is a French. Mr Annan's personal office includes his Pakistani "gatekeeper",Syed Iqbal Riza, a Frenchwoman and a Dane. These senior officials may have been targeted for bugging. While the fight goes on to place a nation's best diplomats in the UN secretariat, their spies are placing their own personnel too.

Some will be inside the UN secretariat, analysing the telegrams destined for Mr Annan's desk. Some may be "political officers" working for the UN weapons inspection agency. Others will be scattered throughout the diplomatic missions accredited to the UN. The extent of the infiltration is not known. It is only when the US expels a diplomat for spying, or when a spy is "outed" that the veil is lifted on such activities.

As Ms Short's allegations swirled around the UN building on the bank of New York's East River, several diplomats were sanguine about what would happen next. One diplomat said: "We'll handle this in the usual way: Kofi will ask for confirmation, he'll call in the Brits, he'll issue instructions to make sure something like this never happens again, and then we'll all go back to business as usual." Another diplomat, when asked what difference the latest spy scandal would make, said: "Nothing."