London, May 1 (Bloomberg) -- The U.S. and U.K. went to war against Iraq because of the Middle East country's oil reserves, an adviser to British Prime Minister Tony Blair said.

Sir Jonathan Porritt, head of the Sustainable Development Commission, which advises Blair's government on ecological issues, said the prospect of winning access to Iraqi oil was "a very large factor" in the allies' decision to attack Iraq in March.

"I don't think the war would have happened if Iraq didn't have the second-largest oil reserves in the world," Porritt said in a Sky News television interview.