Officials at the prime minister's office and MI-6, the foreign intelligence service, have begun a comprehensive review of how to avoid a repetition of the mistakes that led Britain to overestimate Iraq's military threat before the war.

A commission led by Robin Butler, a former chief civil servant, has concluded Britain's pre-war claims that Iraq had stockpiles of weapons of mass destruction were wrong and based largely on flimsy and poorly sourced intelligence.

There has been mixed reaction to the Butler report. Opponents of the Iraq war say it shows Prime Minister Tony Blair used intelligence selectively to make his case against Saddam Hussein. Blair supporters point out the report did not blame the prime minister, or anyone else, for the mistakes.

A former senior civil servant in the defense ministry, Michael Quinlan, told British television the Butler report confirms there was what he calls "a climate of pressure" on intelligence analysts to mold their findings to meet the government's expectations.

"The report brings out that the assessments of the intelligence were too hard, too confident, that the presentation of those assessments was again, too hard, too confident, and that the political account given to them was yet one further stage too hard and too confident," he said. "It beggars belief to suppose that that was quite unrelated to the fact that, here was the government knowing that it might very well have to go to war before long."

The parents of several British servicemen killed in Iraq say they believe the Butler report proves Mr. Blair sent their sons to war on a questionable pretext, and they want the prime minister to apologize.

Mr. Blair's spokesman says that while the prime minister accepts responsibility for the intelligence failures he will not apologize for mistakes made in what the spokesman calls "good faith."