In an exclusive interview, Mr Blix said he expected to be bugged by the Iraqis, but to be spied upon by the US was a different matter. He described such behaviour as "disgusting", adding: "It feels like an intrusion into your integrity in a situation when you are actually on the same side."

He said he went to extraordinary lengths to protect his office and home, having a UN counter-surveillance team sweep both for bugs.

"If you had something sensitive to talk about you would go out into the restaurant or out into the streets," he said.

Mr Blix's darkest fears were reinforced when he was shown a set of photographs by a senior member of the Bush administration which he insists could only have been obtained through underhand means.

His accusations came after the former cabinet minster, Clare Short, claimed that US-British intelligence bugged the office of the UN secretary general, Kofi Annan.

Speaking from his home in Stockholm, Mr Blix said that what galled him most was the possibility of being bugged by a country, the US, that he had assumed was on the same side. He said that surveillance was only to be expected between enemies or in cases where serious criminal activity is being monitored.

"But here it is between people who cooperate and it is an unpleasant feeling," he said.

Mr Blix, a Swedish diplomat who was head of the UN arms inspectors for Iraq between 2000 and 2003, said he had no conclusive evidence that the US bugged him. But his suspicions were raised when he had repeated trouble with his phone connections at his New York home.

"It might have been something trivial or it might have been something installed somewhere. I don't know," he said.

More worrying was a confrontation with a senior member of the US adminstration. Mr Blix said John Wolf, the US assistant secretary of state for non-proliferation, visited him a fortnight before the war broke out at a time when debate was raging over whether there were weapons of mass destruction in Iraq and whether Mr Blix should be given more time to find them.

Mr Wolf presented him with two pictures of an Iraq drone and a cluster bomb, photos Mr Blix believed could only have been secured from within the UN weapons office. Mr Blix said: "He should not have had them. I asked him how he got them and he would not tell me and I said I resented that.

"It could have been some staff belonging to us that handed them to the Americans. I don't think it is very likely but it could have happened - I don't have 100% control of everybody. It could also be that they managed to break into the secure fax and got it that way."

Tony Blair, still feeling the aftershocks of Ms Short's allegations, made little reference to the bugging issue in a speech to the Labour party in Scotland. He did, however, condemn Ms Short for the second day running, accusing her of being in alliance with the Tories.

As well as the claim that Mr Annan was bugged, another former secretary general, Boutros-Boutros Gali, also expressed suspicions yesterday. Richard Butler, a predecessor of Mr Blix as chief UN weapons inspector, joined in too, saying it was "plainly silly" to think his phone calls were not being monitored during his tenure.

The Australian Broadcasting Corporation reported an intelligence official who said Mr Blix's mobile phone calls were routinely monitored from Iraq and the transcripts shared between the British, American and Australian intelligence services.

Mr Blix was inundated with calls from journalists worldwide yesterday. Speaking only to the Guardian, he said he thought it was unlikely it happened in Iraq "because I did not use my mobile phone there. In any case, we were totally aware that Iraqis would have microphones in the walls".

Instead, he expressed his conviction that the UN headquarters in New York was much more likely to have been targeted. "The suspicions have been directed at the Americans for bugging and I think that is more likely in New York in the run-up to the votes in the security council."

Mr Blix was given the job by the UN security council of determining whether Iraq had weapons of mass destruction. His reports to the security council were eagerly awaited for any evidence of a "smoking gun" that would have triggered war. As such, both the US and British governments were keen to know what he had found and was thinking, and what the Iraqis were saying to him.

An international lawyer as well as having been a career diplomat, Mr Blix said legal and moral questions were raised by bugging. The Vienna convention prohibiting such behaviour "should be applicable to the UN headquarters".

Mr Blix, whose book giving an inside account of the run-up to the war with Iraq will be serialised in the Guardian next week, said it was unlikely that the US would have gained any advantage from bugging him: "They might have heard things in a more naked manner than in the diplomatic tones I would use publicly."

But the only information he regarded as ultra-sensitive was the location and timing of surprise inspections of potential Iraqi weapons sites. This would have been of use only to the Iraqis.

Such information was never delivered electronically, he said. "We would never talk about such matters on telephones, never use electronic devices at all. Instructions to inspectors were hand-carried."

Mr Blix, who came out of retirement to lead the UN team, said he had been given the authority by the security council to carry out the job and assumed he had the trust of its members. He was disappointed to find later that the Pentagon was briefing against him. He said the Pentagon had a low opinion of the inspectors as a whole or possibly himself.

He described the suspected bugging as hypocritical: "You are cooperating with the people who sit across the desk one day and if the next they are listening to you, it is an unpleasant feeling."

Asked if it was morally questionable, he replied: "Well, I don't know what morals they have. Questionable, yes."

He challenged the British government's legal basis for going to war in Iraq, in the light of the collapse of the case against Katharine Gun, the former British intelligence officer. When he worked at the UN he was not able to speak out but now he said that the decision to go to war should have been a matter for the whole of the security council, not a minority of it.

Mr Blix is sceptical about whether Iraq had weapons of mass destruction in the period immediately before the war. He now believes that both Mr Blair and President George Bush should have been more open to the evidence emerging from Iraq. "I think we should have had more critical thinking on the part of the political leadership. They should have heard the evidence. They should have heard the dissenting opinions.

"It is one thing to advocate the building of a railroad and you go ahead a little carelessly with the argumentation. But if it is a question of starting a war, one would like to have a more solid basis."

Hans Blix: my story