Sami Salih, The Sunday Telegraph reported, defected to Britain with his wife earlier this year after "masterminding" Saddam's sanctions-busting oil-smuggling network.
Mr Salih, 38, had been accused of spying and was arrested and tortured by Saddam's guards before escaping, the newspaper said. He is now reportedly in hiding in Belgium.
The paper said Mr Salih had given the intelligence services details of the layout of the presidential palace on the banks of the Tigris and Euphrates.
He said that despite the hostility that led to war between Iran and Iraq from 1980 to 1988, Tehran agreed to help Iraq to avoid United Nations sanctions imposed after the Gulf war. He said the Iranians took a cut of the black-market oil profits while both countries used the proceeds to buy weapons.
Both sides worked through front companies and by 1996, when Mr Salih was arrested, the trade was earning about $1m a day for each country.
The Iraqi profits were deposited in Amman, Jordan, and were used to finance Saddam's regime and to buy arms and military supplies. After Mr Salih's arrest, the companies were run by Saddam's sons Uday and Qusay, then shut down.Reuse content