Sir Ivor Roberts, a former British ambassador, told a British newspaper that U.K. diplomats warned pretty much unanimously that invading Iraq was, well, a bad idea:

Every British ambassador in the Middle East warned the Government that invading Iraq would be a "nightmare" and turn popular opinion against the West, a former envoy has told The Daily Telegraph.

To the best of his memory, the assessments offered by Britain's representatives in the Muslim world were unanimous. "Every ambassador in a Middle East post accurately predicted what a nightmare invading Iraq would be," he said.

"The telegrams I saw were full of doom and gloom about the consequences."