Sir Christopher Meyer — ambassador to the United States from 1997 to just before the war — told The Observer in Sunday editions that the advice on postwar planning was ignored.
Meyer's comments emerged amid rising tension in London over the visit there by President Bush this week, which is spurring a massive security operation, attracting thousands of protesters and reviving resentment toward the Iraq war and the U.S. president.
Meyer is a trusted adviser of Prime Minister Tony Blair and an admirer of Mr. Bush, whom he first met he was Texas governor in 1998.
In a column in the Times of London this weekend, Meyer wrote that he learned that Mr. Bush "was indeed far more impressive and fluent than he had been given credit for," and noted "his self-assurance, easy dominance of heavyweight advisers like (national security adviser Condoleezza) Rice and Secretary of State Colin Powell."
But in the interview with The Observer, Meyer said elements in the Bush administration ignored British advice in the run-up to the war.
Meyer said that between the Security Council's passage of a resolution calling for new weapons inspections and the start of the war, British officials regularly told the Americans that more postwar planning was needed.
"One of the things that did not work out between us was a properly agreed strategy," Meyer told The Observer. "I suspect that a lot of things that we were saying to the Americans when we had a number of meetings towards the end of last year on post-Saddam strategy, a lot of those things have now been shown to be right."
While the U.S. has restored many aspects of Iraqi civil life — rebuilding schools, reopening hospitals and restoring power to many areas — the postwar administration has been beset by problems.
The U.S. has lost 281 soldiers since the end of major combat operations on May 1 and 419 troops overall. Few foreign countries are offering new troops and aid agencies have scaled back their operations amid an apparent spike in violence.
The White House recently reversed course on the process for restoring sovereignty to Iraq, agreeing to early elections and a handover this summer. Previously, the U.S. insisted that a constitution be drafted before elections were held.
The Bush administration has also had to ask Congress for $20 billion in reconstruction aid, reversing prewar optimism that, with its huge oil stores, Iraq could pay for its own reconstruction. Iraq's ravaged economy my have unemployment as high as 75 percent.
"I think they were consumed in the contingency planning for war. We were saying that's fine but we must be clear in our own mind what is happening afterwards. That was absolutely indispensable," Meyer said. "The message was well taken in the State Department but it could not agree an approach with the Defense Department and the vice president."
Meyer also told the newspaper that when Blair met Mr. Bush in January, the president said he was ready to attack the following month. Blair wanted to try to get a second U.N. resolution approving the war.
The allies did try to get a second resolution, but abandoned that effort when it was obvious the measure would not pass.