LONDON, July 18 - Less than a month before the London bombings, Britain's top intelligence and law enforcement officials concluded that "at present there is not a group with both the current intent and the capability to attack the U.K.," according to a confidential terror threat assessment report.
The previously undisclosed report was sent to British government agencies, foreign governments and corporations in mid-June, about three weeks before a team of four British suicide bombers mounted their July 7 attack on London's public transportation system.
The assessment by the Joint Terrorist Analysis Center prompted the British government to lower its formal threat assessment one level, from "severe defined" to "substantial." The center includes officials from Britain's top intelligence agencies, as well as its police forces and Customs.
Asked to comment on the document, a senior British official, who spoke on condition of anonymity, said, "We do not discuss intelligence assessments."
British officials said the reduced threat level had no practical impact on terrorism preventive measures, and the British home secretary said it did not make Britain more vulnerable to attack.
The tersely worded threat assessment was particularly surprising because it stated that terrorist-related activity in Britain was a direct result of violence in Iraq.
"Events in Iraq are continuing to act as motivation and a focus of a range of terrorist related activity in the U.K.," said the report, a copy of which was made available by a foreign intelligence service and was not disputed by four senior British officials who were asked about it.
On Monday, Pakistani government officials confirmed that three of the four men identified as the London bombers visited Pakistan last year.
Prime Minister Tony Blair and other British government leaders have sharply criticized claims made since the attacks that the country's support for the American-led war in Iraq and the involvement of British troops in fighting the insurgency there were factors in the terrorist bombings on British soil.
On Monday, the Royal Institute of International Affairs, an influential private research organization commonly known as Chatham House, concluded that Britain's participation in the war in Iraq and as "pillion passenger" of American foreign policy had made it vulnerable to terrorist attack. A pillion is the second seat on a motorcycle.
Mr. Blair and other British leaders have insisted there is no evidence that the policy on Iraq motivated the London bombers. They have argued instead that the coordinated bombing attacks that killed at least 56 people are part of a continuing worldwide campaign of anti-Western violence by Al Qaeda and Qaeda-influenced groups that predates the American-led invasion of Iraq in March 2003.
"The terrorists have struck across the world, in countries allied with the United States backing the war in Iraq and in countries which had nothing whatever to do with the war in Iraq," Jack Straw, Britain's foreign secretary, said Monday in Brussels.
Two groups have claimed responsibility for the attacks, although neither claim has been authenticated. Both mentioned the Iraq war as one of the reasons for the attacks.
By reducing its assessment of the threat, British officials put the possibility of a terror attack by Islamic radicals only one level higher than the current chance of a terror attack by the Irish Republican Army, now ranked as "moderate."
In April of this year, before Britain's general election, the possibility of an I.R.A. attack was ranked as "substantial," the same threat level as an Islamist terror strike before July 7. The last I.R.A. attack in London was a bombing at the Canary Wharf in 1996.
The disclosure of the report's contents comes as some British politicians are calling for an official inquiry into whether the attacks represented a failure of intelligence and whether the investigation has been handled properly.
A senior British official familiar with the deliberations about the threat assessment said there was a sharp disagreement among officials about whether the intelligence justified lowering the threat level. "There was not an easy consensus," said the official, who declined to elaborate.
As the investigation into the terrorist bombings continues, British police officials admitted that a potential suspect had escaped detection two weeks before the bombings because he was not deemed a serious security threat.
The unidentified man, who was on a security "watch list," arrived in Britain several weeks ago, but was not placed under surveillance. He left Britain just hours before the London bombings. British investigators have said he is a suspect in the attacks.
Some British and European counterterrorism officials have raised concerns that at least two of the bombers might have been known to the police as part of two sprawling terrorism investigations in 2004: the investigation of an alleged attempt in the spring to build an enormous fertilizer bomb to strike somewhere in London, and the arrest of a small cell of men in August who were accused of plotting to attack financial buildings in Manhattan, Newark and Washington, D.C.
Questions have been raised, for example, why domestic intelligence agents did not determine that Mohammad Sidique Khan, one of the four bombers, was a threat to national security in 2004. Early last year, Britain investigated him in connection with the alleged plot to build the fertilizer bomb and use it in London, according to several European-based counterterrorism officials. British officials have refused to confirm whether Mr. Khan, 22, of Leeds, was a suspect in that investigation, or answer questions about why they did not monitor his activities.
The fact that the terrorist threat warning had been lowered just weeks before the bombings was widely reported in the news media the day after the attacks. But the rationale for that decision and the reference to Iraq, contained in the confidential report, has not been previously disclosed.
Immediately after the terrorist attacks, top police officials announced that they had had no warning that an attack was imminent. Since then, senior officials have said there was no intelligence developed about an attack using suicide bombers or one aimed at the London Underground.
On the day after the attacks, for example, Home Secretary Charles Clarke was asked about the lowered threat assessment on BBC radio, and replied, "Obviously, it was wrong." Mr. Clarke said the threat level had already been increased, adding, "The fact is, we need to try to get this right."
While the report said there had been no sign of an imminent attack, it also clearly said there was a two-pronged threat facing the country. One threat came from the international Qaeda network, and the other came from indigenous radicals that either draw inspiration from Al Qaeda or act independently, the assessment said.
The threat from Al Qaeda's "leadership-directed plots has not gone away," the report said.
Despite that threat and the situation in Iraq, it added, "many of our current concerns focus on the wide range and large number of extremist networks and individuals in the U.K. and individuals and groups that are inspired by but only loosely affiliated to A.Q. or are entirely autonomous."
The report concluded, "Some of these have the potential to plan U.K. attacks, and it is also possible that lone extremists or small groups could attempt lower-level attacks."
The analysis center that released the assessment is based at the headquarters of MI5, Britain's domestic security service.
Although "substantial" is the fourth highest of seven levels of threat definitions, the assessment memo said it "indicates a continued high level of threat and that an attack might well be mounted without warning."
This compares with "critical," the highest level of alert, which means that an attack is expected within two weeks, down to "negligible," the seventh and lowest level.
Unlike the United States, where threat assessments are made public, Britain uses its own version only as guidance for Scotland Yard and Britain's infrastructure, including hospital and transport systems, as well as for foreign governments and multinational corporations that could be targets.
Some foreign intelligence officials and foreign corporate executives with operations in London said they were surprised when they learned last month that Britain's threat assessment had been lowered.
"It was a surprise for me that suddenly, one day, after two or three years, it changed," said a European-based intelligence official who would not allow his name to be used because officials who work for the intelligence agencies are required by the rules of their agencies to remain anonymous. "I said to myself, 'Oh, my God, what happened?' "