The first criminal charges have been laid over allegations that Australian company Leighton Holdings won a $US733 million contract in Iraq by bribing the country's oil ministers and other high-ranking officials.

On Wednesday morning, Britain's Serious Fraud Office charged two middlemen hired in 2010 by Leighton's international arm to secure an oil pipeline contract in Iraq.

The Eclipse, one of Leighton's fleet of multimillion-dollar oil and gas pipe-laying barges.

The charging by British authorities of the two Leighton middlemen raises fresh questions about the failure of Australian police to lay a single bribery charge in connection to one of the nation's longest-running corporate crime scandals.

Federal agents have spent seven years investigating Leighton's international arm – which has been renamed CIMIC – along with several of its former top overseas executives.